fire-cracked rock features on sandy landforms in the northern rocky mountains: toward establishing...

Fire-Cracked Rock Features on Sandy

Landforms in the Northern Rocky

Mountains: Toward Establishing Reliable

Frames of Reference for Assessing

Site Integrity

Alston V. Thoms*

Department of Anthropology, Texas A&M University, College Station,

Texas 77843

In cool coniferous forest settings of the Northern Rocky Mountains, well-preserved fire-crackedrock (FCR) features within 30 cm of the surface on ostensibly stable, sandy upland landformsdate to the last six millennia. Isolated FCR and artifacts sometimes extend a meter or morebelow surface, which is suggestive of in situ burial. A paucity of intact features in the lowersolum, however, is consistent with the downward migration of deeply buried artifacts by bio-mechanical processes, especially floralturbation. Moreover, an absence of credible sedimentsource areas usually precludes colluvial deposition, and results of grain-size analysis reportedherein are inconsistent with eolian deposition. Site disarticulation rates tend to be faster onlandforms in warmer forested regions of south-central North America, given that most intactFCR features there date only to the last two millennia. The very presence of millennia-old FCRfeatures in these diverse settings, however, is a testament to their durability and utility as meas-ures of site integrity. © 2007 Wiley Periodicals, Inc.

INTRODUCTION

It behooves archaeologists to study upland sites because so much of the pastunfolded in upland settings. Implementation of such studies, however, is a scientificchallenge in that upland settings tend to undergo net erosion and, other thingsbeing equal, sites there are likely to be poorly preserved compared to those in allu-vial bottomlands. A substantial body of geoarchaeological data has been compiledand synthesized about impacts to archaeological sites from pedoturbation, butconsiderable epistemological debate remains about site integrity issues at uplandsites (e.g., Wood and Johnson, 1978; Burtchard, 1987; Schiffer, 1987; Johnson andWatson-Stegner, 1990; Bocek, 1992; Leigh, 2001; Balek, 2002; Frederick et al., 2002;Johnson, 2002; Peacock and Fant, 2002; Van Nest, 2002).

In forested settings, pedoturbation tends to be dominated by biomechanicalprocesses, primarily floralturbation, that lead inevitably to the disarticulation of

Geoarchaeology: An International Journal, Vol. 22, No. 5, 477–510 (2007)© 2007 Wiley Periodicals, Inc.Published online in Wiley Interscience (www.interscience.wiley.com). DOI:10.1002/gea.20169

*E-mail: [email protected]

GEA225_610_20169.qxp 3/21/07 2:40 PM Page 477

archaeological deposits. The dynamic character of sandy soils on ostensibly stablelandforms is shown by vertical and lateral displacement of artifacts that, in turn,provides glimpses into early stages of the formation of biomantles, stone zones, andstone-lines (Johnson 1990, 2002; Leigh, 2001; Balek, 2002). Sandy landforms understudy here, primarily high Pleistocene terraces, are said to be “stable” insofar as thereis little to suggest substantial deposition or erosion on the treads. There has been,however, appreciable erosion along the margins of flat-lying landforms, and localizedeolian reworking likely resulted from periodic denudation following forest fires.

This article calls attention to the widespread presence of durable (i.e., resilient inthe face of site disarticulation processes) fire-cracked rock (FCR) features buriedin stable upland landforms with dynamic sandy soils that support forest vegetation.It also addresses a question of equifinality that pertains to whether the presence ofartifacts well below the depth of most FCR features is likely attributed tobiomechanical processes or to deposition by eolian and/or colluvial processes. Idraw heavily from my experiences investigating FCR features at hunter-gatherersites in the Northern Rocky Mountains (Figure 1a) (Thoms, 1984a, 1989, 2003, 2006;Thoms and Burtchard, 1987). These archaeological experiences chronicle my effortsto begin to understand what Donald Johnson (2002:35) calls the “biomechanicalmessage” in his seminal article “Bioturbation, Dynamic Denudation, and the Powerof Theory.” My intent is to demonstrate that FCR features are reliable ecologicalframes of reference (cf. Binford, 2001) for interpreting the integrity of floralturbatedarchaeological records encased in forest-covered, sandy upland landforms. Towardthat end, this paper reviews the general nature of sites and FCR features in the studyarea, provides detailed information about the vertical distribution of FCR featuresand artifacts at selected sites, and presents the results of artifact distribution andparticle-size analyses to illustrate the role of biomechanical processes in the burialof artifacts on sandy landforms.

STUDY AREA: NORTH AMERICA’S NORTHERN ROCKY MOUNTAINS

In North America, sandy upland landforms occur in diverse biogeographicalsettings throughout the continent. Their widespread distribution affords an oppor-tunity to examine and compare FCR feature preservation on similar landformsin places with decidedly different, but largely unquantified, rates of bioturbation.Among the sandy landforms in comparatively northern latitudes (ca. 48–49�) wheresite formation processes have been studied are Pleistocene terraces, fans, anddunes along lower valley walls in the Northern Rocky Mountains (Mierendorf,1984; Burtchard, 1987; Mierendorf et al., 1987; Thoms and Burtchard, 1987).Denuded examples of these landforms and their archeological deposits wereexposed in a 5,000-acre drawdown zone of the U.S. portion of Lake Koocanusa,a hydroelectric-generating reservoir that is lowered annually in anticipation ofspring runoff (Thoms, 1984a). The reservoir occupies the middle reach of theKootenai River valley for some 145 km, with about 100 km being within north-west Montana and the remainder in south-central British Columbia, Canada(Figures 1b and 1c). The southern two-thirds of the U.S. portion of the reservoir

THOMS

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 22, NO. 5 DOI: 10.1002/GEA478

GEA225_610_20169.qxp 3/21/07 2:40 PM Page 478

DOI: 10.1002/GEA GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 22, NO. 5

FIRE-CRACKED ROCK FEATURES ON SANDY LANDFORMS

479

Figure 1. The Northern Rocky Mountain study area: (a) physiographic map of NorthAmerica showing the general location of the study area and other areas discussed in thetext (courtesy of National Atlas of the United States, December 8, 2000; http://nationalatlas.gov);(b) map of Lake Koocanusa area showing sites discussed herein; (c) Lake Koocanusa(middle reach of the Kootenai River Valley, northeastern Montana), looking north towardthe Tobacco Plains from the upper canyon zone; (d) a tree well that resulted from forestfire on a kame terrace that burned out an old ponderosa pine stump; (e) Calispell Valley,northwestern Washington; and (f) ponderosa pine roots exposed along a cut bank in theCalispell Valley (author’s photographs).

GEA225_610_20169.qxp 3/21/07 2:40 PM Page 479

lie in a narrow valley termed the canyon zone, which includes upper and lower sec-tions; the northern third lies within a wide valley known as the Tobacco Plains(Roll, 1982a).

The Northern Rocky Mountain province is of one of several physiographic subdi-visions in the Rocky Mountain System. The case study area is the now-inundatedmiddle Kootenai River valley (Figures 1a–1c). Most ranges in the Northern Rockies,including the Purcell and Salish mountains that surround the middle reach of theKootenai River, are composed primarily of the Precambrian Belt Supergroup ofmetasedimentary and metadiorite deposits, along with Cretaceous and Tertiarygranitic rocks (Roll, 1982a; Stratling et al., 2000).

Precipitation is winter-dominant throughout the Northern Rockies. On and nearvalley floors, it ranges from about 38 to 64 cm per year (ca. 15 to 25 inches), most ofwhich occurs as snowfall, and the growing season is less than 90 days (Roll, 1982a;Schalk and Mierendorf, 1984; Mierendorf, 2000). Elevations of the valley floors andlower walls, where sites discussed herein are located, range from about 610 to 760 mabove mean sea level (ca. 2,000 to 2,500 ft). Western needleleaf forests dominatemost of the Northern Rocky Mountains, and potential natural vegetation in the middleKootenai Valley is classified as western ponderosa (Pinus ponderosa) forest (Küchler,1964). Today, Douglas-fir (Pseudotsuga douglassi) grows in abundance on the valleyfloors and on terraces and fans along the lower walls. Case study sites are locatedon late Pleistocene-aged landforms—terraces and dunes—with southern solarexposures. Native vegetation probably consisted of scattered ponderosa pine,Douglas-fir, bunch grasses, and herbaceous and woody plants (Mierendorf, 1984;Schalk and Mierendorf, 1984).

In such settings, tree roots occupy a significant part of the subsurface (Figure 1f).When trees are blown down, their tipped-up roots disrupt corresponding portions ofthe archaeological record (cf. Johnson and Watson-Stegner, 1990). It is also importantto consider the role of forest fires in pedoturbation and site disarticulation. Dependingon setting and forest type, fires occurred once every 4 to 250 years prior toEuroAmerican settlement, and they played the key role in maintaining open-standforests so characteristic of the Northern Rockies under Native American occupation(Arno, 1980; Gruell, 1983; Mehringer, 1985). Fires that burn tree stumps and rootstypically leave the ground pockmarked by “wells” where tree boles burned and bylinear depressions where near-surface roots burned (Figure 1d). These cavities areconduits for downward displacement of artifacts.

In the Northern Rockies and other settings where forest vegetation has prevailedthrough the millennia, it is axiomatic that floralturbation will be the primary bio-mechanical force and that biomantle formation, including floralmantles, will becountermanded significantly by tree uprooting (cf. Wood and Johnson, 1978; Budy,1987; Burtchard, 1987; Schiffer, 1987). In its sediment-mixing role, forest-levelfloralturbation fosters regressive pedogenesis (i.e., soil haploidization), especiallyby disrupting E horizon formation and substantially disturbing B horizons (Johnsonand Watson-Stegner, 1990). Overall, however, progressive pedogenesis (i.e., soilhorizonation) predominates, although exposures of forest soils invariably showdisrupted horizons and root casts in varying states of preservation.

THOMS


GEA225_610_20169.qxp 3/21/07 2:40 PM 80

BIOMECHANICAL CONTEXTS FOR FEATURE DISARTICULATION

Working with his students and colleagues, Johnson has emphasized the paramountimportance of bioturbation as a soil-formation agent and its archaeological relevance(Wood and Johnson, 1978; Johnson, 1990). His complex, dynamic denudation processmodel highlights bioturbation as a process on par with anthropogenic, geomorphogenic,and other pedogenic processes (Johnson, 2002). The bioturbation component of thismodel focuses on the continuous roles of soil biota (e.g., animals, plants, fungi, bacteria)in loosening soil and of soil fauna, including worms, ants, and termites, in bringingfine-grained sediment to the surface. This process creates a biomantle, which is oftencoincident with A and E horizons, especially those underlain by a Bt horizon.

If not countermanded by tree uprooting and large-animal turbation, which bringlarge artifacts and natural cobbles and boulders to the surface, “biomechanicalloosening causes large clasts to gravitationally settle downward relative to the finesoil fraction, wherein a stone-line often forms near the base of the biomantle”(Johnson, 2002: 8). In some mid-continent areas, tree throws are believed to resultin disturbance of the total soil surface within 3,000 to 5,000 years. In forested settingseverywhere, the downward movement of particles is also facilitated by slow soilagitation, through wind-caused tree sway, and slow volume and pressure increasesvia root growth, as well as by subsurface channels left by normal root decay (Johnsonand Watson-Stegner, 1990: 544–551). According to this model, and presuming wide-spread usage of hot-rock cooking technology, disarticulated remains of millennia-oldFCR features (i.e., isolated pieces of FCR) should be distributed throughout theactive bioturbation zone.

The speed at which readily observable stone-lines form varies through time andacross space, but the general process is similar in all but the most extreme environ-ments on Earth (Johnson, 2002). In South Africa, for example, Acheulean tools morethan 150,000 years old are incorporated into natural clast stone-lines in silty depositswithin 50,000 years and comparatively shallow ceramic lines (“stone-lines” composedof pottery sherds) develop in just over a thousand years (Johnson, 2002: 21, 27). Ingeneral, relatively fast rates of bioturbation and resulting biomantle and stone-lineformation, are likely to characterize moist, temperate forest ecosystems, such asthose in southeast North America, where gross primary production (i.e., total rate ofphotosynthesis) is estimated at 8,000 kilocalories (KCAL)/m2/year (Odum, 1971: 51).Substantially slower rates should occur in markedly cooler coniferous forest ecosys-tems, such as the Northern Rocky Mountains, where gross primary production isestimated at 3,000 KCAL/m2/year (Odum, 1971: 51).

So compelling have been analytical results supportive of upland site burial bybiomechanical processes that Balek (2002:49) recently concluded, “Burial of most,if not all, artifacts in stable upland soils developed in pre-Holocene sediments innonfeature contexts, is due to vertical movement of the artifact in response to normalbiological activity, namely burrowing and mounding by earth worms, ants, and otherfauna, and by tree uprooting.” An example of these patterns in a grassland setting isfound at the Jasper Ridge site, a thousand-year-old hunter-gatherer site located ona sandy terrace in the foothills west of San Francisco Bay, California, where Barbara



481

GEA225_610_20169.qxp 3/21/07 2:40 PM Page 481

Bocek studied site disarticulation impacts from gophers. Hearths and “rockconcentrations” were present in the upper part of the profile. Extensive faunaltur-bation was evidenced by isolated pieces of FCR found throughout the 1.2 m thick artifact-bearing stratum, but mostly between 30 and 60 cm below surface(Bocek, 1986: 596–599).

FCR features more than a thousand years old also are preserved in the upperportion of the solum at upland sites in coniferous forest ecosystems of the PacificNorthwest (e.g., Schalk and Meatte, 1988; Thoms, 1989, 1998, 2006; Mierendorf et al.,1998) as well as in deciduous forest ecosystems of south-central North America (e.g.,Thoms et al., 1994; Rogers and Kotter, 1995; Fields, 2004). The widespread presenceof intact and disarticulated FCR features in biogeographically diverse forest settings,where floralturbation is rampant, suggests that complete feature disarticulation is amillennia-long process. Accordingly, FCR features at upland sites are expected toexhibit varying states of preservation, depending on their relative age and nuances ofpedoturbation. The scientific challenge is to extract reliable information about howpeople used the uplands from these invariably bioturbated sites.

THE NATURE OF FCR FEATURES

For biomechanical messages about FCR feature preservation to be heuristicallyuseful requires reliable information about the general nature and use of hot-rockcooking facilities. Such information is available in ethnographic accounts from theNorthern Rockies and from results of actualistic experiments. Of interest here areobservations and interview data compiled by Allan Smith in 1936 and 1937 during hisextensive fieldwork at the Kalispel Reservation in the Calispell Valley of northeastWashington (Figures 1a and 1e). Smith’s fieldwork among the Kalispel people wasundertaken only a few decades after white immigrants settled the region and whenolder members of the Indian community could still report on hunter-gatherer cookingstrategies, which were soon replaced by non-Indian practices. His ethnographicaccounts remained in manuscript form until portions thereof appeared as a chapterin a multivolume report documenting results of a large-scale cultural resourcesmanagement study carried out during the 1980s in advance of a newsprint-millconstruction project near the Kalispel Reservation (Andrefsky et al., 2000).

Smith (2000) described six basic types of cook-stone facilities, versions of which weresurely used by hunter-gatherers throughout the Northern Rockies and beyond: (1) earth oven in a shallow pit with rocks heated therein; (2) earth oven in a shallowpit with rocks heated in a nearby hearth; (3) surface oven or hearth with rocks heatedtherein; (4) steaming pit with rocks heated in a nearby hearth; (5) stone boiling in apit with rocks heated in a nearby hearth; and (6) stone boiling in above-groundcontainers with rocks heated in a nearby hearth. Table I summarizes information aboutbasic construction and cooking techniques used in hot-rock cookery, as well as the typesof food cooked in those facilities. Throughout North America, ethnographic data(e.g., Driver and Massey, 1957) also attest to a diversity of cooking facilities with stone heating elements. Most of these features, however, are variants of earth ovens,

THOMS


GEA225_610_20169.qxp 3/21/07 2:40 PM Page 482

Ear

th o

ven

in a

sha

llow

,cl

osed

pit

; roc

ks h

eate

dth

erei

n (a

ka s

team

-roa

stin

g pi

t)(S

mit

h, 2

000:

7.8

–7.1

5)

Ear

th o

ven

in a

sha

llow

ope

npi

t; r

ocks

hea

ted

near

by (

aka

roas

ting

pit

) (S

mit

h, 2

000:

7.14

–7.1

6)

Surf

ace

oven

; roc

k(s)

hea

ted

ther

ein

(aka

dry

ing

oven

)(S

mit

h, 2

000:

7.2

0)

Cam

as (

Cam

assia

qu

am

ash

)w

ild o

nion

(A

lliu

m,

spp.

),un

nam

ed r

oots

, bla

ck t

ree

liche

n (A

lecto

ria

frem

on

ti)

Bea

r, d

eer,

and

mea

t of

any

kind

, as

a fi

rst

step

in d

ryin

gpr

oces

s or

for

imm

edia

teco

nsum

ptio

n

Bea

r, d

eer,

oth

er m

eat,

as

fina

lst

ep in

dry

ing

proc

ess

(for

eat

-in

g la

ter)

For

cam

as (

othe

r fo

ods

prob

ably

coo

ked

in s

mal

ler

oven

s*),

a r

ound

(ca

. 2.4

–3.1

mdi

a., 0

.15

m d

eep)

or

ellip

tica

l pit

(ca

. 2.1

� 1

.5 �

0.1

5 m

) is

dug

and

som

etim

es li

ned

wit

h ro

cks

(ca.

0.1

7 m

dia

); a

larg

e qu

anti

ty o

f fi

rew

ood

(sti

cks

and

som

e lo

gs 0

.15

mdi

a.)

is a

dded

and

the

n an

othe

r la

yer

of r

ocks

; the

woo

d pi

le is

fir

ed, b

urns

dow

n, t

hehe

ated

roc

ks a

re s

prea

d ac

ross

the

bot

tom

of

the

pit;

gre

en b

ough

s, g

rass

, or

skun

kca

bbag

e le

aves

are

use

d to

cov

er t

he h

ot r

ocks

and

coa

ls; c

amas

bul

bs a

re a

dded

(in

wov

en s

acks

or

bask

ets,

but

con

tain

ers

repo

rted

ly n

ot u

sed

whe

n bl

ack

tree

lich

en is

cook

ed w

ith

cam

as o

r on

ions

), t

hen

cove

red

wit

h gr

een

plan

t m

ater

ial a

nd f

inal

lyw

ith

eart

h; s

omet

ime

a fi

re is

bui

lt o

n to

p of

the

low

mou

nd a

nd q

uick

ly c

over

ed w

ith

sod

to k

eep

the

woo

d fr

om b

urni

ng t

oo f

ast;

and

fin

ally

, ano

ther

laye

r of

ear

th is

adde

d to

hol

d in

the

hea

t (u

pper

fir

e no

t us

ed w

hen

blac

k tr

ee li

chen

was

incl

uded

wit

h ca

mas

or

onio

ns);

the

bul

bs c

ook

for

48 h

ours

bef

ore

the

oven

is o

pene

d.

A s

hallo

w p

it is

dug

, sim

ilar

in s

hape

but

sm

alle

r th

an t

hat

used

for

cam

as; h

ot r

ocks

,he

ated

in a

nea

rby

fire

, are

pla

ced

in t

he p

it a

nd c

over

ed w

ith

gree

n bo

ughs

on

whi

char

e pl

aced

larg

e pi

eces

of

mea

t th

at a

re c

over

ed w

ith

addi

tion

al g

reen

bou

ghs

orgr

ass

and

allo

wed

to

cook

for

ca.

30

min

utes

, in

prep

arat

ion

for

subs

eque

nt d

ryin

g or

ston

e bo

iling

, if

cons

umpt

ion

is im

min

ent;

for

pit

-coo

king

mea

t ca

. 20

min

utes

for

imm

edia

te c

onsu

mpt

ion:

a la

rge

num

ber

of h

ot, f

lat

rock

s ar

e pl

aced

in t

he b

otto

m o

fth

e pi

t, co

vere

d w

ith

gree

n bo

ughs

on

whi

ch is

pla

ced

mea

t cut

into

str

ips,

whi

ch in

turn

ar

e co

vere

d w

ith

a la

yer

of g

reen

bra

nche

s w

eigh

ted

dow

n w

ith

unhe

ated

roc

ks.

A la

rge

rock

is h

eate

d in

pla

ce, p

resu

mab

ly b

y a

fire

bui

lt o

n th

e su

rfac

e, a

nd, a

fter

the

fire

bur

ns d

own

(pre

sum

ably

the

rem

aini

ng c

oals

are

scr

aped

aw

ay t

o av

oid

burn

ing

the

gree

n-bo

ughs

cov

erin

g th

e ro

ck),

it is

cov

ered

by

gree

n br

anch

es u

pon

whi

ch is

pla

ced

the

half

-roa

sted

mea

t, b

oth

of w

hich

are

the

n co

vere

d w

ith

gree

nbo

ughs

hel

d in

pla

ce b

y a

few

col

d ro

cks;

the

mea

t is

coo

ked

unti

l dry

or

abou

t 30

min

utes

.

Tab

le I

. Su

mm

ary

of e

thno

grap

hica

lly d

ocum

ente

d ho

t-ro

ck c

ooki

ng f

acili

ties

use

d by

the

Kal

ispe

l peo

ple,

mon

tane

hun

ter-

gath

erer

s of

nor

thea

stW

ashi

ngto

n an

d no

rthe

rn I

daho

(m

odif

ied

from

Tho

ms,

200

3b).

Hot

-roc

kF

oods

pre

pare

dco

okin

g fa

cilit

ies

in t

he f

acili

tyB

asic

con

stru

ctio

n an

d co

okin

g te

chni

ques

for

the

fac

ility

(con

tin

ued)

GEA225_610_20169.qxp 3/21/07 2:40 PM Page 483

* C

omm

ents

in b

rack

ets

are

the

pres

ent

auth

or’s

“w

orki

ng id

eas,

” as

opp

osed

to

info

rmat

ion

com

pile

d fr

om S

mit

h’s

data

.

Stea

min

g pi

t; w

ith

rock

she

ated

nea

rby

(aka

ste

amin

gov

en)

(Sm

ith,

200

0: 7

.19–

7.20

)

Ston

e-bo

iling

pit

; wit

h ro

cks

heat

ed n

earb

y (S

mit

h, 2

000:

7.16

–7.1

9)

Ston

e-bo

iling

con

tain

er, a

bove

-gr

ou

nd

co

nta

iner

; w

ith

ro

cks

hea

ted

nea

rby

(Sm

ith

, 20

00:

7.16

–7.1

9)

Egg

s an

d sm

all a

mou

nts

ofro

ot f

oods

Mam

mal

s, b

irds

, re

ptil

es,

fish

,eg

gs, m

any

root

foo

ds, b

erri

es,

and

teas

Sam

e as

in s

tone

-boi

ling

pits

Hot

roc

ks (

som

etim

es o

nly

one

larg

e fl

at r

ock)

are

hea

ted

in n

earb

y fi

re a

nd p

lace

din

a s

hallo

w p

it (

pres

umab

ly b

asin

-sha

ped,

ca.

0.7

5 m

in d

ia. a

nd 0

.3 m

dee

p) a

ndco

vere

d w

ith

gree

n tw

igs

or g

rass

; foo

d is

add

ed a

nd c

over

ed w

ith

a la

yer

of g

reen

gras

s; a

sti

ck is

pla

ced

upri

ght

in t

he p

it a

nd t

he w

hole

is c

over

ed w

ith

eart

h; t

hest

ick

is t

hen

rem

oved

and

a li

ttle

wat

er is

add

ed t

hrou

gh t

he r

esul

ting

hol

e, w

hich

isth

en c

over

ed, a

nd t

he f

ood

allo

wed

to

cook

.

A b

ucke

t-sh

aped

(ne

ar-v

erti

cal s

idew

alls

) pi

t is

dug

, ca.

0.3

m in

dia

. and

0.1

–0.3

mde

ep, a

nd li

ned

wit

h in

ner

bark

fro

m a

n ev

ergr

een

tree

, or

som

etim

es a

dee

r pa

unch

and

rare

ly a

n un

tann

ed h

ide;

wat

er is

add

ed u

ntil

the

cont

aine

r-lin

ed p

it is

abo

ut h

alf

full,

and

the

n th

e fo

od, c

ut in

to s

mal

l pie

ces,

is a

dded

; hot

roc

ks “

of a

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open-air griddles, and steaming and stone-boiling pits (Figure 2). Importantly, each ofthese feature types is manifested by a discrete concentration of FCR.

A similar array of cook-stone features is known archaeologically to vary consid-erably in size and morphology and to have been used throughout the Holocene to boil,roast, steam, and bake a variety of animal and plant foods (e.g., Thoms, 1989, 1998,2003; Black et al., 1997). Composed mainly of large clasts (ca. 5–25 cm), FCR featurestend to be structurally durable in subsurface worlds of dynamic denudation, espe-cially when compared to features defined by fine-grained matrices, such as rocklesshearths and ash-filled pits, or by concentrations of flakes, shells, and other small



485

Figure 2. Examples of generic cook-stone facilities typical of those used in western North America: (a) closedearth oven with a fire-in-situ rock heating element; (b) closed steaming pit with cook stones heated outsidethe pit; (c) open-air, hot-rock griddle; and (d) stone-boiling pit and surface fire for heating cook stones.

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artifacts. Judging from ethnographic data on hot-rock cookery, the vertical distri-bution of FCR at a given site at the time of abandonment is readily predictable:(1) FCR scatters are expected to occur on the surface of a given activity area and/orin nearby disposal areas, as would be expected of artifact distributions in general;and (2) FCR concentrations representative of a variety of hot-rock heating elementsin the bottoms of shallow pits are expected to occur at depths between 15 and 30 cmbelow surface. What is especially distinctive about FCR as a class of artifacts is thatits initial vertical distribution was likely bimodal: surface scatters and subsurfaceconcentrations.

Useful data pertaining to feature function and integrity can also be extracted fromindividual pieces of FCR. Thermal-weathering studies, for example, have revealedinformation about how cooking stones may have been used (Schalk and Meatte, 1988;Jackson, 1998). Pieces of FCR heated experimentally to 800 �C and cooled graduallyfor 48 hours to simulate earth-oven cooking exhibit evidence of intensive weathering(e.g., cracking, oxidation, and loss of bulk density) compared to moderate weather-ing of cooking stones heated similarly and cooled gradually for 24 hours to simulatehot-rock griddle cooking in an open hearth. Rocks heated to 800 �C and cooled quicklyby immersion in water, to simulate stone boiling, exhibited far less thermal weatheringthan those that cooled gradually (Jackson, 1998). Paleomagnetic analysis of individualpieces of FCR has proven useful in identifying rocks that were heated and cooled inplace, as is expected of an intact earth-oven heating element, or a rock griddle in asurface hearth. This type of analysis can also identify rocks that were heated in oneplace and cooled in another, as would be the case for cooking stones used in stoneboiling or some types of pit steaming (Gose, 2000, 2006).

METHODS FOR ADDRESSING EQUIFINALITY

ISSUES OF SITE BURIAL

There is often a question of equifinality regarding whether artifacts on sandyupland landforms were buried by biomechanical processes inherent in pedoturbationor by eolian sedimentation (Burtchard, 1987; Mierendorf et al., 1987; Frederick et al.,2002; Thoms, 2002, 2006). David Leigh (2001) aptly addressed this issue in an articlesubtitled “Techniques for Evaluating Pedoturbation versus Sedimentation.” He iden-tified several key indicators of a predominance of biomechanical agents in artifactburial in North America’s eastern woodlands: (1) presence in the solum of measur-able amounts (0.02%) of �2 mm particles and/or substantial silt or clay (�10%); (2) vertical and horizontal displacement of artifacts and features; (3) a positive rela-tionship between depth of pedoturbative artifact burial and time, such that oldermaterials, in general, tend to be buried deeper than younger items; and (4) an absenceof intact features (Leigh, 2001).

A geoarchaeological context for assessing site integrity issues is provided byanalyses of the vertical distribution of artifacts and natural clasts at several highterrace sites in the study area. The intent here is to distinguish between site burialby eolian sedimentation versus bioturbation. Other things being equal, the pat-terned distribution of “cultural” clasts buried in situ (i.e., occupation zones and

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levels) should be readily distinguishable from that of “natural” clasts, regardlessof whether natural clasts were buried by sedimentation or pedoturbation processesof any kind.

At 24LN410, one of the case study sites located on a forested terrace above the LakeKoocanusa drawdown zone (Figure 1b), comparisons are made between the verticaldistributions of natural clasts—iron concretions developed in the Bs (Bir) horizonand pebbles—and cultural clasts—chipped stone debitage and FCR. The intent hereis to address equifinality issues pertaining to the burial of an FCR feature 60 cmbelow surface, which is more than twice the depth of all other excavated FCR featuresin the study area.

To further address equifinality-of-deposition issues at 24LN410, I conductedparticle-size analyses of sediments from the test pit that yielded the deeply buriedfeature and compared the results to sediment analyses at two sites where the modeof sediment deposition was not in question: (1) 24LN804, a high terrace site in theTobacco Plains zone along the Tobacco River, where profiles revealed that artifact-bearing sediments were glacio-fluvial/lacustrine in origin and consisted of thin,well-stratified beds of fine sand and silt; and (2) 24LN691, a site on a sand dunein the Kootenai Flats area of the Tobacco Plains.

To better understand site formation processes, I also built experimental features,with rocks and associated artifact scatters, on sandy landforms in the LakeKoocanusa drawdown zone, as well as on a sandy, forest-covered (ponderosa pine)kame terrace above the lake at our experimental archaeology grounds (EAG) inthe Kootenai National Forest (Figure 1b) (Thoms, 1995a). My goal over the nextdecade or more is to monitor rock and artifact movements that result from reser-voir-related processes, bioturbation, forest fires, graviturbation, and other disar-ticulation forces. Experimental features in the drawdown zone are destined mainlyfor wave-caused and eolian erosion. Experimental features in flat-lying areas andon slopes at the EAG are intended to assess impacts from bioturbation and gravi-turbation. Several features built around small trees are intended to assess impactsfrom tree growth.

To study impacts from forest fires, I constructed features and artifact scattersadjacent to several 30-year-old tree stumps at the EAG. I anticipated that one ormore of the stumps would burn out when the Forest Service conducted controlledburns of the property and that, in the process, I might have an opportunity todocument feature disarticulation. Any tree stumps that did not burn out wouldprovide an opportunity to monitor long-term feature displacement that resulted fromthe gradual decay of old snags. Preliminary results are presented later in this paperfor one case where an experimental feature was significantly impacted when thestump burned out and created a tree well.

In addressing site integrity and equifinality-of-deposition issues, an archaeologicalcontext is established by reviewing the general nature of sites and FCR features inthe study area. Toward that end, the following section summarizes informationobtained from selected sites in the drawdown zone and on vegetated terraces thatabutted Lake Koocanusa. Sites in the denuded drawdown zone often containedhorizontally well-preserved lag deposits of artifacts and features. In many cases, the



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wave action removed the soil matrix, giving the sites an appearance of having beenexcavated with cultural materials left in place. Test excavated sites on forestedlandforms around the lake also contained a variety of features in various states ofpreservation. In those cases, however, the surrounding fine-grained matrix was inplace and the impact from living tree roots was readily observable.

SITES AND FCR FEATURES IN THE MIDDLE KOOTENAI VALLEY

An opportunity to study upland sites in the middle Kootenai Valley came in the early1980s with the discovery of more than 100 archaeological sites on denuded sandylandforms along the valley walls as much as 87 m above the floodplain (Thoms,1984a). Late Pleistocene and early Holocene terraces (T4–T7), fans, and dunes alongthe valley walls and the accompanying archaeological sites were exposed within a5,000-acre drawdown zone of the U.S. portion of Lake Koocanusa (Figure 1b).Geomorphic and archaeological studies revealed that the Kootenai River downcutto its present elevation by about 9,000 radiocarbon years ago and that terraces aboveT2 as well as the fans and dunes on those terraces were formed prior to the fall ofMount Mazama tephra, about 6,700 radiocarbon years ago (Cochran and Leonhardy,1982; Mierendorf, 1984; Mierendorf et al., 1987).

Site preservation conditions in the drawdown zone varied considerably but, ingeneral, horizontal site structure was well preserved, although most artifacts andmany of the features had been displaced vertically as a result of reservoir-relatederosion. Among the best-represented features were FCR concentrations thatappeared to be remains of oven-cooking and stone-boiling activities. Many of thesefeatures contained small pieces of burned and unburned bone and chipped stone(Thoms, 1984a).

In 1994 and 1995, I returned to the study area with Texas A&M University fieldschool students to excavate several comparatively well-preserved features in thedrawdown zone and to conduct surveys and test excavated sites on forest-coveredlandforms along the reservoir’s margins. Most of the tested sites were located on ahigh kame terrace (T13) north of the Tobacco River. Others were located on a highfluvial terrace (T8). All of the FCR features were found within 25 cm of the surface,and most of them were impacted by modern tree roots (Jackson and Clabaugh, 2006;Thoms, 2006). As was the case for well-preserved features in the drawdown zone,those above the reservoir also contained burned and unburned pieces of chippedstone and bone.

Denuded Sites in the Drawdown Zone

At most sites in the Lake Koocanusa drawdown zone, reservoir-caused erosionremoved the O, E, and part of the B horizons, which compose the upper 15–25 cmof the solum and include the biomantle, assuming it was present. As noted, mostartifacts exposed on the denuded surfaces were lag deposits, but a few FCR featuresrecorded in the 1980s on unusually flat-topped terraces in the drawdown zone appeared to be fairly intact heating elements (i.e., FCR concentrations) that

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probably originated between 10 and 30 cm below surface (Thoms, 1984b, 1984c).A few FCR features on flat-topped landforms in the drawdown zone were still in goodcondition when they were test excavated in the mid-1990s (Thoms et al., 1995;Thoms, 2006).

That many sites retained a substantial degree of integrity, in spite of inundationimpacts and prior floralturbation, is indicated by the presence of horizontallydiscrete FCR features at half of the sites in the drawdown zone. Approximately500 FCR features were recorded at 100 sites, usually only one or two per site, butoccasionally there were more than 20 (Thoms, 1984b). Most of these features wereaffected, to one degree or another, by wave action that removed much of the fine-grained matrix, leaving larger clasts vertically displaced but fairly intact horizon-tally (Thoms, 1984c).

Some of the best-preserved FCR features were found at high terrace sites thatoverlooked the mouth of the Tobacco River in the northern part of the TobaccoPlains (Figure 1b). Two adjacent sites on the tread of T7, 24LN792 and 24LN804 hadFCR features typical of well- and moderately preserved features in the LakeKoocanusa drawdown zone (Figures 3a, 3b, and 4). In this setting, two decades ofseasonal drawdowns and accompanying erosion resulted in removal of only theO and E horizon (termed A 2) sediments in a few unusually flat places and therebyexposed fairly intact rock heating elements still embedded in the lowermost portionof the E and uppermost B horizons (Thoms et al., 1995; Thoms, 2006).

Eighteen FCR features in various states of preservation were recorded on thedenuded surface of 24LN792 in 1994 (Figures 3a and 3b). A side-notched arrowpoint, an adze-like tool, a pestle, numerous pieces of FCR, chipped stone debitage,and burned bone fragments were also scattered across the site. Several featureson flat ground were fairly well preserved, including Feature 1, which consisted of a relatively solid (i.e., clast-supported) lens of FCR about 1.2 m in diameter(Figures 4a and 4b). This feature was sampled by excavating a 1.0 � 0.5 m test pitto 20 cm below the drawdown surface. All cultural materials were recovered fromthe upper 10 cm of excavated sediments. Oxidized sediments underlay the FCR andappeared to have resulted from a burned tree stump or large root rather than fromuse of the feature per se (Figure 4b). Thermal-weathering analysis of a sample ofrocks from the feature showed considerable variation in weathering intensity but,overall, there was a high degree of thermal stress (Jackson and Clabaugh, 2006), aswould be expected of rocks in an earth oven used for prolonged cooking. Bonefragments from Feature 1 and the adjacent nonfeature area yielded a conventionalradiocarbon age of 890 � 60 B.P. (Thoms et al., 1995). This feature was interpretedas the well-preserved remains of an earth-oven heating element.

Four of the five FCR features recorded at 24LN804 were on gentle slopes or lowrises where the lower part of the B horizon was exposed (Figures 3a and 3b). Thesefeatures were vertically displaced, horizontally dispersed, and they contained lit-tle or no chipped stone or bone fragments. Feature 1, located in a flat-lying area,was more compact and contained notably more bone fragments that the otherfeatures. It was partially buried by post-reservoir sediments and represented byseveral pieces of FCR and a partially exposed elk antler tine.



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Figure 3. The Tobacco Plains area, Lake Koocanusa: (a) view to the north showing thelocations of archeological sites and other places discussed in the text (author’sphotograph); (b) site map of 24LN792 and 24LN804 (redrawn from Thoms et al., 1995:Figure 24).

A 1.0 � 0.5 m test pit dug to 20 cm below surface sampled Feature 1 and revealeda dispersed lens of FCR within an area about a meter in diameter. Several pieces ofFCR were exposed on the surface within a few meters of the feature. The large elkantler tine was weathered similarly to antlers recovered at other sites in the draw-down zone and hence plausibly associated temporally with the feature. An unspent,modern .22 cartridge found within the FCR concentration reminded us that spatialproximity does not equate with temporal association. Carbon-stained sediment waspresent within and just below the FCR and extended to a depth of at least 20 cmbelow surface in a pattern suggestive of an infilled tree well or root channel. All ofthe FCR was recovered from within 5 cm of the denuded surface (Figures 4c and 4d).Paleomagnetic analysis of several large pieces of FCR from this feature suggeststhat the rocks were heated in place and slightly displaced after they had cooled

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491

Figure 4. Fire-cracked rock features at 24LN792 and 24LN804: (a) oblique view of Feature 1, 24LN792(photograph courtesy of Center for Ecological Archaeology); (b) profile of Feature 1, 24LN792 (redrawnfrom Thoms et al., 1995: Figure 28); (c) oblique view of Feature 1, 24LN804 (photograph courtesy ofCenter for Ecological Archaeology); (d) profile of Feature 1, 24LN804 (redrawn from Thoms et al., 1995:Figure 34).

(Gose, 2006). Thermal-weathering analysis showed considerable variation inweathering intensity, but overall a moderate degree of thermal stress, consistentwith that expected of an earth oven or open-air griddle used for a few hours (Jacksonand Clabaugh, 2006).

Site 24LN1054 is the most artifact-rich site within a cluster of sites in the drawdownzone near the mouth of Bristow Creek in the lower canyon zone. It is especially wellknown for its middle and early Holocene projectile points (Thoms, 1984c; Thomsand Burtchard, 1987). The site is located on a sandy, ridge-like terrace remnant (T6)approximately 61 m (200 ft) above the Kootenai River (Figure 5a). As with mostsites in the drawdown zone, wave and wind erosion during seasonal drawdowns

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Figure 5. Bristow Creek area, Lake Koocanusa: (a) sites, landforms, and the drawdown zone (author’sphotograph); (b) topographic map of 24LN1054 showing test pit locations (redrawn from Mierendorfet al., 1987: Figure 9–4); (c) density of fire-cracked rocks exposed on the denuded surface of 24LN1054(redrawn from Thoms, 1984c: Figure 11–14).

resulted in the removal of the O and most of the E (A2) horizon sediments, composingthe upper 15–25 cm of the solum (Figures 5b and 6a). B horizon sediments remainedalong the crest of the eroded ridge where most of the artifacts were exposed.Exposures of C horizon and exposed roots indicated that a meter or more of sedimenthad been eroded from some slopes (Figure 5a).

Artifact density at 24LN1054 decreased with depth regardless of artifact size.A few flakes were recovered from the C horizon, as much as 1.9 m below the

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denuded surface and in excess of 2 m below the pre-reservoir surface (Figure 4d).Isolated FCR was recovered from depths greater than 1.0 m below the erodedsurface, but the vast majority of FCR occurred on the eroded surface, especiallyalong the ridge crest, as was the case with all artifact types (Figure 5c). When thesite was first documented by archaeologists, many discrete FCR features wereobserved on the surface, but the spatial integrity of these features was subse-quently destroyed by relic hunters in search of projectile points. Well-preservedfeatures were present, however, on adjacent terrace remnants that were lessattractive to collectors, presumably because significantly less chipped stonedebitage was exposed on the surface, as was the case at 24LN1058 (Figure 5a)(Thoms, 1984b).

The vertical distribution of artifacts at 24LN1054 suggested the possibility ofsignificant eolian deposition during the Holocene. Moreover, there was a weaktendency for correct chronological ordering (i.e., cultural stratigraphy) of projectilepoint types: (1) seven of eight late Holocene arrow points and about 30 late-to-early Holocene dart points were recovered from the eroded surface or embeddedin near-surface, reservoir-disturbed sediments representing remnants of the O, E,and uppermost B horizons; (2) two mid-Holocene dart points occurred in the Bs(i.e., Bir) horizon; (3) excavations in the B/C horizon yielded seven mid-to-earlyHolocene dart points; and (4) one mid-to-early Holocene dart point and onelate Holocene arrow point fragment came from the upper part of the C horizon(Burtchard, 1987).

The vertical distribution of Mazama glass shards at 24LN1054 was also consis-tent with a model of Holocene eolian deposition accompanied by bioturbation. The highest percentage of shards occurred in the middle and lower portions of theB horizon, ca. 20 to 60 cm below the denuded and eroded surface, with a few shardsfound in the overlying and underlying portions of the solum (Figure 6b) (Mierendorfet al., 1987).

Buried FCR features were not discovered during the initial round of excavationsat 24LN1054 (Thoms, 1984c), nor were they encountered in any of the 15 test pitsexcavated across the site during the second round of testing (Figure 5b). Most of the15 test pits dug in 1986 were placed to sample subsurface anomalies identified duringa proton magnetometer survey. Excavation revealed that all of the magnetic anomalieswere attributable to burned sediments and charcoal readily associated with rootcasts in various states of preservation (Burtchard and Thoms, 1987; Hathaway, 1987).Elsewhere in the Northern Rockies, including in the Calispell Valley of northeastWashington, proton magnetometer surveys proved successful in locating buriedearth ovens with intact and disturbed rock heating elements (Andrefsky et al., 2000;Hathaway et al., 2000).

Sites Along the Reservoir Margins

Sites along the reservoir margin contained a similar array of feature types to thoseexposed in the drawdown zone. Chipped stone debitage and burned and unburnedbone fragments were common in both settings. Edge-modified flakes and projectilepoints were the most common tool types at sites above as well as within the reservoir’s



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drawdown zone. Approximately 40 FCR features were identified at 22 sites in forestedsettings. With the exception of one feature at 24LN410, all of these features werefound within 20 cm of the surface.

The vertical distribution of artifacts at 24LN424, a site in the Tobacco Plains zone,illustrates the pattern observed at most sites along the reservoir margins (Figures 3c and3d). Artifacts commonly occurred from the surface to 50 cm below surface, but thehighest density, by far, was between 20 and 30 cm below surface. FCR was recoveredfrom the upper 30 cm in several dozen 50 � 50 cm test units, with the highest densityoccurring in the first 10 cm, which was about 10 cm higher in the profile compared tomost other sites. The vertical distribution of artifacts at 24LN880 and a few other siteswas similar in that chipped stone and FCR extended from the surface to 50 cm belowsurface, but the highest density of chipped stone was in level one (0–10 cm below sur-face). The highest density of FCR at 24LN880 occurred in level two, between 10 and20 cm below surface, as was the case at most sites (Figures 3a, 3c, and 3d).

Excavation units at 24LN882, another site in the Tobacco Plains zone, exposedseveral FCR features that exemplified near-surface features found at most sites alongthe reservoir’s margins. Features 1 and 2 illustrate two of the feature types commonlyfound at these sites. Feature 1 at 24LN882 was a well-preserved concentration of FCRthat appeared to be in a small pit about 20 cm deep (Figures 7a and 7b). Thermal-weathering analysis showed slight to moderate levels of weathering intensity (Jacksonand Clabaugh, 2006), which is consistent with stone boiling. Morphologically, thisfeature also fits expectations for a concentration of boiling stones in a shallow pit.

Feature 2 at 24LN882 was a concentration of bone fragments and comparativelydispersed FCR between 10 and 20 cm below surface (Figure 7b). Thermal-weatheringanalysis showed considerable variation in weathering intensity, but most rocks exhib-ited a moderate to high degree of thermal stress (Jackson and Clabaugh, 2006). Theavailable data do not point to a specific type of cooking function, nor do they excludethe possibility that FRC concentration is part of a sheet-midden deposit of generalcamp debris.

Test excavations were also carried out at 24LN410, a low-density site of undeter-mined age situated on a forested remnant of T8, near 24LN1054 (Figures 1b and 5a)in the lower canyon zone. As with most high terrace sites, 24LN410 was bestrepresented on the terrace tread near the scarp (Figure 8a). The back side of thesite abutted a linear, low-lying area, possibly an in-filled late Pleistocene channel, thatseparated the site from the valley wall proper and effectively precluded alluvial orcolluvial deposition on the terrace tread.



495

Figure 6. Stratigraphic information data, artifact, and natural-clast distribution data for selected sites inthe middle Kootenai Valley: (a) type profile and description of soil horizons at 24LN1054 (redrawn andupdated from Mierendorf et al., 1987: Figure 9–10); (b) vertical distribution of Mazama glass shard at24LN1054 (redrawn and updated from Mierendorf et al., 1987: Figure 9–2); (c) vertical distribution, by soilhorizons of different-sized chipped stone debitage at 24LN1054 (redrawn and updated from Mierendorfet al., 1987: Figure 9–12); (d) density of chipped stone artifacts per 10 cm level below surface at 24LN410,424, and 882; (e) density of FCR per 10 cm level below surface at 24LN410, 424, and 882.

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The vertical distribution of artifacts at 24LN410 was anomalous compared toother sites along the reservoir’s margins. In this case, the distribution of chippedstone was somewhat bimodal, with highest density of artifacts between 40 and 50 cmbelow surface and a moderate density between 70 and 80 cm below surface(Figure 3c). FCR density peaked between 50 and 60 cm below surface. In marked con-trast to all other sites, 24LN410 contained an FCR feature (No. 1) buried between55 and 65 cm below surface (Figure 8).

All of the FCR in Feature 1 at 24LN410 was found within a slightly carbon-stainedarea that appeared to have resulted from a root burn(s). Wood charcoal spatiallyassociated with the FCR concentration yielded a conventional, uncalibrated radio-carbon age of 680 � 40 years B.P. (Beta 182164). As interpreted, the radiocarbon ageattests to the age of the root burn, as opposed to the FCR feature per se (Figure 8c).Among the approximately 30 pieces of FCR in Feature 1 were several fractured butarticulated pieces of rock. Paleomagnetic analysis of six pieces of FCR, including

THOMS


Figure 7. Fire-cracked rock features from other sites discussed in the text: (a) Feature 1, 24LN882, a pos-sible stone-boiling pit feature with FCR (photograph courtesy of Center for Ecological Archaeology);(b) Feature 2, 24LN882, an amorphous concentration of fire-cracked rocks, possibly representing remainsof a disturbed open-air hearth or discarded stone-boiling rocks (photograph courtesy of the Center forEcological Archaeology); (c) intact heating element of a well-preserved earth oven, dated to 3,460�/�70B.P., at 45PO139, Calispell Valley, northeast Washington (Thoms, 1989: 402) (author’s photograph); (d) anintact heating element, embedded in carbon-stained sediment and dated to 2,930�/�100 B.P. at CVAP-45,Calispell Valley, northeast Washington (Thoms, 1989: 387) (author’s photograph).

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whole and fractured but articulated specimens, indicated that these stones had beenheated, cooled, and randomly redeposited, insofar as none of them showed similarmagnetic alignments relative to their resting places (Gose, 2006). Thermal-weatheringanalysis indicted moderate levels of weathering, which is consistent with stone boil-ing (Jackson and Clabaugh, 2006).

ASSESSMENTS OF FEATURE INTEGRITY

During the mid-1980s, hundreds of test pits and shovel probes were excavated atdozens of denuded drawdown-zone sites in search of buried, intact FCR features, butnone were found (Thoms, 1984b). Archaeologists also examined thousands of metersof wave-caused cutbanks along the margins of the reservoir without finding a singlecultural feature buried more than 25 cm below surface (Thoms, 1984b; Timmons,1994). That virtually all FCR features in the reservoir area appear to have beenconstructed on the pre-reservoir (i.e., modern) surface strongly suggests that therewas very little eolian or colluvial deposition on most sandy landforms along thevalley wall during the Holocene.

The abundance of FCR on the denuded surface at 24LN1054 attests to thepresence at times in the past of FCR features buried in the upper 25 cm or so ofthe pre-reservoir solum. Test excavations at this site and a few others in the draw-down zone demonstrated that a considerable quantity of cultural material wasburied well below the near-surface FCR features and scatters (Thoms, 1984b, 1984c;Thoms and Burtchard, 1987). Lack of buried features at these sites, however, does



497

Figure 8. Site 24LN410: (a) topographic map showing locations of test pits; (b) north wall of Test Pit 1showing soil horizons and root disturbance (author’s photograph); (c) graph of vertical distribution of arti-facts (3.2 mm screen) and natural clasts (1 mm mesh) from Test Pit 1, with profile/planview of Feature 1.

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not preclude the possibility of site burial by wind-blown sediments, but their apparentabsence is consistent with the expected results of site burial by biomechanicalprocesses.

As with 24LN1054, artifacts at 24LN410 were buried in greater numbers at greaterdepths than was the case at most other sites on forest-covered, high terraces. Whatwas unusual about 24LN410 was that it contained the deepest buried FCR featureknown in the study area. Discovery of this deeply buried feature (ca. 55–65 cm belowsurface) kept a door open to the possibility of site burial by millennia-old eoliandeposition. Although not especially likely in a coniferous forest setting, localizedeolian deposition probably occurred when sandy alluvium was exposed and reworkedfollowing forest fires that denuded the local landscape.

Several factors suggested the possibility that Feature 1 and other cultural materialsrecovered between 40 and 70 cm below surface at 24LN410 were buried by post-occupation eolian deposition: (1) the visually well-sorted and massive nature of theupper meter of sandy solum; (2) a paucity of gravel in the sandy deposit; and (3) anabsence of alluvial bedding in the portion of the C horizon exposed in test pits.However, had these test pits been dug a meter deeper, they would have encounteredwell-stratified sandy and silty alluvium that comprises the terrace fill in this part ofthe valley (Mierendorf, 1984). As noted, the presence of a linear, low-lying area,perhaps a paleochannel, between the valley wall and terrace tread effectivelyprecluded the possibility of colluvial deposition.

Sediment Analysis Results from 24LN410

Test Pit 1 at 24LN410 exemplified a bimodal pattern in the vertical distribution ofartifacts at the site. In this particular test pit, sediments screened through 3.2 mm mesh(1/8-inch) showed density peaks at 10–20 cm below surface and at 50–60 cm belowsurface. Natural clasts—iron concretions (formed in the Bs2 horizon) and smallpebbles recovered from 1 mm mesh—showed a similar distribution pattern(Figure 8c). In Test Pit 1, the lower peak in artifact density resulted primarily froma linear-shaped FCR concentration (Feature 1) that occurred between 55 and 65 cmbelow surface. Carbon-stained and faintly oxidized sediments, along with a few smallpieces of wood charcoal, were encountered between 20 and 70 cm below surface andinterpreted as the product of a burned-out root channel. Given that burned-out rootchannels and tree wells are associated with many near-surface, in situ FCR featuresin the study area, it remained plausible that Feature 1 was also in situ.

Particle-size analysis of upper 60 cm of the solum in Test Pit 1 at 24LN410 revealedthe following: (1) there were only a few particles of very coarse sand; (2) total sandcomprised 56.1 to 57.8 percent of the sample; (3) total silt comprised from 34.9 to 38.2 percent; and (4) total clay comprised from 5.4 to 8.6 percent (Table II). A similar grain-size distribution was obtained from sediments in the upper 70 cm inSondage E1 at 24LN804, a site in the Tobacco Plains zone located on a high terracewith pedogenically modified, well-stratified fluvial deposits: (1) there were a only afew particles of very coarse sand; (2) total sand comprised 62.3 to 43.9 percent of the

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sample in the A, Bs, and BC horizons, and 16.7 percent in the C horizon; (3) total siltcomprised from 50.2 to 33.9 percent in the A–BC horizons and 27.7 percent in theC horizon; and (4) total clay comprised from 6.0 to 2.9 percent.

A very different particle-size distribution, with total sand composing at least 82 percent of the samples, was obtained from the upper 150 cm of deposits inSondage B2 at 24LN691, a site located on a sand dune in the Tobacco Plains zone:(1) there was no very coarse sand in the sample; (2) total sand comprised 81.9 to89.6 percent of the sample; (3) total silt comprised from 6.7 to 13.5 percent; and(4) total clay comprised from 2.4 to 4.6 percent. The underlying well-stratified flu-vial deposits at 24LN691, from 2 to almost 3 m below surface, contained: (1) novery coarse sand; (2) 92 to 96.6 percent total sand; (3) 2.1 to 5.0 percent total silt;and (4) 1.3 to 3.0 percent total clay.

Results of these particle-size analyses show that artifact-bearing sediments at24LN410 are far more similar in texture to those from a bioturbated, glacio-fluvial/lacustrine context than they are to those from a bioturbated eolian context.It is likely that the subdivision of the Bs horizon at 24LN410 (Figure 8) representedpedogenically modified fluvial deposits, as was the case at 24LN804. Given thatnatural pebbles, iron concretions, chipped stone debitage, and FCR had similarvertical distribution patterns, site burial by biomechanical means is more likely thanby eolian or alluvial sedimentation. The relative paucity of natural clasts and artifactsin the upper 10 cm of the site is also consistent with the idea of an incipient biomantle.The marked increase in frequency of debitage and iron concretions between 10 and20 cm below surface may represent an incipient stone zone. The overall decrease inthe density of larger clasts, including FCR and chipped stone debitage, below 20 cmis consistent with artifact burial by floralturbation.

Burned Stump Results from the EAG

I have not yet excavated any of the experimental features and artifact scattersconstructed in the drawdown zone or at the EAG (Figure 9a), although I plan to doso within the next several years. However, a visual inspection made after thecontrolled burn at the EAG revealed impacts to one basin-shaped FCR feature thathad been built adjacent to an old stump (Figure 9b). When the stump burned, itcreated a tree well about 80 cm in diameter and 40 cm deep, with open root chan-nels extending more than a meter below surface. A portion of the experimentalfeature—at least 4 of 20 rocks—had fallen into the resulting tree well, and two in situfeature rocks were visible in the sidewalls (Figure 9c). The redeposited rocksappeared to be arranged as a clast-supported, sand-covered rock pile 40 cm belowsurface (Figure 9d). Oxidized and carbon-stained sediments were abundant in the treewell, but none of the visible feature rocks were fire-broken.

DISCUSSION

Available data from 24LN410 on the vertical distribution of artifacts and the particle-size analyses are consistent with a scenario that the modern surface

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501

Figure 9. Artificial rock features and artifact scatters at the Experimental Archaeological Grounds,Kootenai National Forest, Montana: (a) example of a rock feature in a basin-shaped shallow pit and asso-ciated artifact scatter; (b) old tree stump, adjacent to which a rock feature and artifact scatter wereburied; (c) the same tree stump after it burned out, resulting in the partial displacement of the artificialrock feature; (d) total-station-transit profile of the rock feature and its vertically displaced rocks (author’sphotographs).

and near-surface sediments are one and the same as when hunter-gatherers encampedthere thousands of years ago. In other words, a preponderance of evidence reviewedherein indicates that the uppermost part of the solum in forested settings undergoesconsiderable biomechanical “reworking” and in that respect, it resembles a shallowplow zone wherein fine-grained sediments and large clasts cycle between the surfaceand subsurface (cf. Van Nest, 2002: 60). This cycle is frequently interrupted, however,when gravity translocates artifacts and fine-grained sediments deeper into the solumvia burned-out root channels and cavities created by decayed roots.

To the degree that natural pebbles, iron concretions, chipped stone debitage, andFCR have similar vertical distribution patterns at 24LN410, site burial by biome-chanical means is more likely than by eolian or colluvial sedimentation. The relativepaucity of natural clasts and artifacts in the upper 10 cm of the site is consistentwith the idea of an incipient biomantle, and the marked increase in frequency ofdebitage and iron concretions between 10 and 20 cm below surface may representan incipient stone zone. Moreover, the overall decrease in the density of larger clasts,including FCR and chipped stone debitage, below 20 cm is consistent with artifact

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burial by long-term floralturbation (i.e., throughout the Holocene). The unusualdepth of chipped stone and FCR at this site remains poorly understood, but it couldbe due to an unusual number of forest fires and resulting tree wells coupled with inter-mittent occupation throughout the Holocene, as is the case with nearby 24LN1054.

In light of the ethnographic and archaeological data reviewed herein, which demon-strate that heating elements in cook-stone features typically originated within 25 cmof the surface, it seems unlikely that Feature 1 at 24LN410 was originally constructed55–65 cm below surface. A more reasonable explanation, consistent with results of ourtree-stump-burn experiment, is that this particular heating element originated in theupper portion of the solum and subsequently fell or rolled into a tree well or hardenedchannels created by a burned-out root. In any event, our experimental work clearlyrevealed the potential of tree-stump/root burns to disperse FCR and other artifacts ameter or more below their point of origin and hence well into the C horizon.

Given the evidence that a single tree burn can disarticulate and disperse a feature,it seems evident that forest fires and tree throws over the course of several millenniacould well account for the vertical distribution of artifacts at 24LN410 and 24LN1054.As argued here, disturbed near-surface FCR features and surface scatters are thesource areas for deeply buried artifacts. Considering the probable long-term impactsfrom tree throws and natural stump and root decay, it is a wonder that features sur-vive at all in the upper 25 cm of the solum, let alone in the numbers that are knownto exist throughout the region.

At most sites in the drawdown zone, artifacts and features were exposed on wave-truncated B horizons that, prior to inundation, would have been 30–50 cm belowsurface. “Surface” surveys in the drawdown zone and test excavations at sites thereinyielded more than 200 dart and arrow points. These artifacts attest to widespread,albeit sparse, occupation during the early, middle, and late Holocene (Thoms, 1984a).What is especially noteworthy here is that almost all of the temporally diagnostic arti-facts were found on denuded, wave-truncated B horizons of high terraces, alluvialfans, and dunes. In a very few cases, most notably 24LN1054, several temporallydiagnostic projectile points were also recovered from buried contexts in roughlycorrect stratigraphic order (Thoms, 1984b, 1984c; Thoms and Burtchard, 1987).

The prevailing archaeological wisdom in the 1980s was that mid-Holocene andolder cultural materials excavated from a meter or so below surface at sites on sandyupland landforms had been buried by slowly accumulating eolian deposits(Mierendorf, 1984; Thoms and Burtchard, 1987). This working model was based, inpart, on the vertical distribution of volcanic-glass shards from a massive eruption ofMount Mazama in the central Cascades of Oregon that took place some 6,700 radio-carbon years ago, when the climatic regime was warmer and drier than today andhence conducive to eolian processes. The vertical distribution pattern of MountMazama shards on pre-Holocene, stable, sandy upland landforms is generally asfollows: (1) a low density of shards in the uppermost sediments, typically the O andE horizons, ca. 0–30 cm below surface; (2) a comparatively high density of shards inunderlying B horizon sediments, ca. 30–60 cm below surface; and (3) a near absenceof shards in the C horizons, as was the case at 24LN1054 (Mierendorf, 1984;Mierendorf et al., 1987).

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Although we were reluctant in the late 1980s to reject the possibility of site burialat 24LN1054 by eolian deposition, we tentatively concluded the following: (1) ratesof deposition were slow enough during the last 7,000 years that cultural materials,including FCR, remained exposed on the surface for long periods of time, perhaps acentury or more, and were subject to re-use by the site’s occupants; (2) treefalls,forest fires, and the natural decay of “snags” through the millennia left surface depres-sions that filled with surrounding sediments, including cultural materials; (3) theseprocesses, along with relic-hunting activities, lead to the disarticulation of FCRfeatures; and (4) in spite of these shortcomings, the site “retains enough of its strati-graphic integrity to be useful as a data base for the study of long-term land usesystems” (Burtchard and Thoms, 1987: 470–471).

In light of analytical results presented here, the buried Mazama glass shards at24LN1054 (Thoms and Burtchard, 1987) are accounted for more readily byfloralturbation than by an eolian-deposition model. Processes that facilitate thedownward movement of glass shards include soil agitation by wind-caused treesway, slow volume and pressure increases via root growth, and gravity-induceddisplacement through subsurface channels left by normal root decay (cf. Johnson andWatson-Stegner, 1990). Albeit negative evidence, the apparent absence of any primarydeposits of Mazama tephra in high terrace fill is also consistent with the model of siteburial by biomechanical processes.

Additional support for a biomechanical model comes from: (1) abundant evidencefor floralturbation in the form of innumerable tree roots and root casts in varyingstates of preservation; (2) projectile points characteristic of the entire Holocene,found in lag contexts on wave-truncated B horizons; (3) weak cultural stratigraphyat a few sites, including 24LN1054, as evidenced primarily by most buried arrowpoints being found in the upper part of the solum and numerous dart points beingrecovered from the lower B and upper C horizons; (4) an overall decrease in artifactdensity between 20 and 70 cm below surface, corresponding in general to a depth-related decrease in density of visible roots and root casts; and (5) an absence ofburied FCR features in the lower Bs, BC, and C horizons. Tree throws and stump/rootburns provide ready mechanisms for the translocation of artifacts down the profileand for feature disarticulation in general (Johnson and Watson-Stegner, 1990). Asargued herein, the longer an artifact rests on the surface of a forested sandy landform,the greater the probability it will fall into a tree well or down a root cavity, otherthings being equal. As Leigh (2001) and Thoms (1995b) have pointed out at sites onsandy landforms in the southeast and south-central parts of North America, respec-tively, among the long-term results of forest-level floralturbation is the recreationof weak, temporally correct cultural stratigraphy.

Although the radiocarbon ages for FCR features discussed here fall within thelast thousand years, there are much older features in the upper part of the solumat sites elsewhere in the reservoir area. For example, a carbon-stained featurewith numerous burned bone fragments and a few pieces of FCR on the denudedsurface of a sand dune in the drawdown zone yielded a conventional age of 3200 � 100 yr B.P. (Thoms, 1984c: 285). In the Calispell Valley of northeasternWashington (Figures 1a and 1d), where environmental conditions during the



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Holocene were similar to those in the middle Kootenai Valley, large earth ovenswith rock heating elements within 30 cm of the surface were dated from as early as5510 � 130 yr B.P. to as late as 550 � 120 yr B.P. (uncorrected ages), with most fea-tures dating between 800 and 3200 yr B.P. (Figures 7c and 7d) (Thoms, 1989: 402, 432).

That almost all radiocarbon ages from intact, near-surface cook-stone featureson stable, sandy landforms in the Northern Rockies are less than 4,000 years oldprovides an indication of the amount of the time required for biomechanical processesin general to completely homogenize most sites (Thoms, 1989, 2002). This time framefits well with data reported by Johnson and Watson-Stegner (1990) from forestedlandscapes in the mid-continent area, where tree throws can lead to disturbance ofthe total soil surface within 3,000 to 5,000 years. The implication here is that inforested settings most intact features are likely to be only a thousand years old orso, other things being equal. Given the ubiquitous presence on the regional land-scape of projectile points dated throughout the last 11,000 years or so, the age ofintact FCR features per se does not provide a reliable estimate of the period of humanoccupation or, for that matter, of the onset of hot-rock cookery.

Another measure, albeit indirect, of site burial rates by bioturbation comes froma site on a forested Pleistocene terrace in the Calispell Valley of northeast Washington(Figure 1a). There, a thin lens of volcanic ash, probably from an eruption of MountSt. Helens (set T) about A.D. 1800, or perhaps an unknown ash fall as much as 570years ago, formed the uppermost portion of the mineral soil in almost 40 percent ofthe shovel tests (Thoms, Olson, and Wyss, 1988; Cochran, 1992: 61). Field archaeol-ogists in the interior Pacific Northwest often encounter a lens of St. Helens set-T ashin similar stratigraphic positions. What this suggests is that on sandy landforms inthe Northern Rockies, site burial by biomechanical and other pedoturbation processesmay not be well underway for several centuries and that several millennia may berequired to bury very many artifacts very deep. In marked contrast, Darwin’s exper-iments in England showed that lenses of lime and coal cinders spread on a grass-covered surface were buried by earthworm activity as much as 7.5 cm below surfacewithin 10 years (Darwin, 1896; cited in Balek, 2002). At a site in South Carolina,35 percent of the crushed shells deposited on the surface as fertilizer in the early1800s had been displaced below the plow zone, presumably by bioturbation, within120 years after the fields were abandoned and became forest covered (Mitchie, 1990,cited in Leigh, 2001).

That site disarticulation rates are slower in the Northern Rockies than in warmerparts of the continent also seems apparent in light of other findings. For example,Van Nest (2002) reports that Archaic-aged FCR occurred in abundance some 35 cmbelow surface at a silty sediment case study site in Illinois, but intact features morethan 2,500 years old were apparently lacking altogether. She attributed these patternsto biomantle and stone-zone formation. In the Post Oak Savannah region of southeastTexas, along the southwestern border of the continent’s temperate forest ecosystem(Figure 1a), intact cook-stone features more than 2000 years old are seldom found inthe upper 30 cm on stable, sandy landforms, but scattered FCR is common. Intactcook-stone features, however, are found buried more than 30 cm below surface by

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alluvial, colluvial, and eolian sedimentation and are known to date throughout thelast 8,000 years (e.g., Rogers and Kotter, 1995; Fields, 2004).

The radiocarbon age—680 � 40 yr B.P.—obtained from charcoal in the root castassociated with Feature 1 at 24LN410 also serves as an indirect measure of rates ofbioturbation in the cool regions of the Northern Rockies. This particular root castwas very distinct in profile and little impacted by horizonization. It still containeda considerable quantity of charcoal and loose fill (Figure 8c). Charcoal from similarlydistinct root casts on a high, partially forested, late Pleistocene sandy terrace alongthe Red River in north-central Texas dated to 120 � 80 yr B.P. Charcoal from a poorlydistinct root burn on the same landform dated to 330 � 90 yr B.P. The oldest isolatedpieces of charcoal found in the B horizon at the site, presumably representing thor-oughly disarticulated root burns, dated to 530 � 60 yr B.P. (Thoms, 1994). Whereasthese ages cannot be said to represent rates of pedogenic overprinting of root castsor biomechanical disturbances per se, they do provide another indication that sitedisarticulation rates are faster in comparatively well-watered and warmer southernparts of the continent than they are in the Northern Rocky Mountains.

CONCLUSIONS

It is reasonable to conclude from the preponderance of evidence reviewed herethat throughout the Holocene most artifacts deposited on the surface of ostensiblystable, sandy landforms in the Northern Rocky mountains are eventually mixed intothe upper 20–30 cm of the profile, including the lower E and uppermost B horizons,by tree throws, stump/root burns, natural decay, and various other biomantle for-mation processes. Open root channels created by continuous tree throws, stump/rootburns, and natural root decay provide ready conduits into the B/C and C horizons forartifacts and other large clasts. That such processes in fact operate to disarticulatecook-stone features, and sometimes reconstitute them deeper in the profile, is shownclearly by our stump-burn experiment at the EAG. It follows, then, that the longeran upland site is on a forested sandy landform, the greater the likelihood that arti-facts and features from a given occupation will be translocated down the profile viafloralturbation and other biomechanical processes.

I have argued elsewhere (Thoms, 1995b: 108–111) that such millennia-longfloralturbation in the Southeast part of the continent leads to “reconstituted culturalstratigraphy.” Mitchie (1990, cited in Leigh, 2001: 281) referred to this hypothesizedphenomenon as “stratification of cultural horizons.” As argued herein, the roughlytemporally correct stratigraphic position of projectile points at 24LN1054, as deter-mined by depth below surface and soil horizonization, is exemplarily of reconstitutedcultural stratigraphy. That this explanation is plausible for sandy landforms in forestedsettings in general is also attested to by the vertical distribution of temporally diagnosticartifacts at Washington-on-the-Brazos, a historic/prehistoric site located on a Pleistoceneterrace with sandy fill in Texas’s inner Gulf Coastal Plain. In this subhumid, subtropi-cal, savannah setting, 6 percent (n 32) of the early 20th-century wire nails were buriedat depths greater than 40 cm below surface, as opposed to 28 percent (n 155) of the



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late 19th-century cut nails and 65 percent (n 1,419) of the prehistoric chipped stonedebitage (Thoms, 1995b: 125).

It is worth noting that if we focus too much on biomechanical messages, we riskoveremphasizing the site disarticulation effects of bioturbation. The danger thereinwould be to conclude, erroneously, that almost all sites buried in stable, sandyupland landforms in the middle Kootenai Valley are likely to be so disturbed as topreclude extraction of significant archaeological information. The widespread occur-rence of cook-stone features in various states of preservation on stable, sandy land-forms in the project area, however, arguably attests to roughly corresponding degreesof site integrity. Moreover, the comparative durability of these features in the face ofbiomechanical disturbance renders them bastions of land-use information that meritconsiderable geoarchaeological attention. Effective utilization of cook-stone featuresas reliable measures of site integrity and sources of cultural information, however,mandates sound and biogeographically specific ethnographic and experimentaldata on the diversity of hot-rock cooking facilities likely to have been used in agiven setting.

Funding for Lake Koocanusa archaeological projects was provided primarily by the U.S. Army Corps ofEngineers, Seattle District, and the Kootenai National Forest, as well as through field schools conductedthrough the Department of Anthropology, Texas A&M University. During the course of fieldwork, RebeccaTimmons, Cindy Hemry, Robert Mierendorf, and Greg Burtchard freely shared their knowledge of Kootenaicountry archaeology. Mike Crow and Patricia Clabaugh revised and formatted the graphics herein. Earlierversions of this paper benefited from discussions with and review comments by Robert Mierendorf, DavidRice, Rhonda Holley, Nancy DeBono, and Patricia Clabaugh. Peer-review comments and suggestions byRolfe Mandel, Evan Peacock, and Loren Davis substantially improved the quality of this article.

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Received September 15, 2003Accepted for publication November 10, 2006

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