Colorado Plateau Province

“Asked to explain what makes the Colorado Plateau unique, geographers grow cryptic, enigmatic, even mystical.”

-Ray Wheeler, “The Colorado Plateau Region”

ARIZONA

Phoenix

Flagstaff

•

Mogollon Rim

Tucson•

Colorado Plateau: a distinct mass of continental crust for >500 million years

Long sedimentary history +

little deformation (long, stable history) =

“layer cake geology”

Volcanic activity mostly confined to edges of Colorado

Plateau

San Francisco Peaks volcanic field near Flagstaff

Shiprock, New Mexico (volcanic neck)

Major uplift of Colorado Plateau 15 - 5 million years ago => Major downcutting by rivers => Deep

canyons, exposing the sedimentary layers

How Grand Canyon was built

EVENT

Sediments deposited, then buried and metamorphosed

Long period of erosion levels land surface

WHEN

2 - 1.8 billion yrs ago (bya)

1.7 - 1.6 bya

PRODUCT

Vishnu Schist

The Great Unconformity

How Grand Canyon was built

EVENT

Sea goes in, sea goes out... Sea goes in, sea goes out...

Mountain-building in Rockies sheds sediments onto Colo. Plateau

WHEN

Paleozoic (590 - 250 million yrs ago (mya)

Mesozoic (250 - 65 mya)

PRODUCT

Thick sequence of marine sandstones, shales, limestones

Thick sand dune deposits, e.g. Navajo Sandstone

How Grand Canyon was built

EVENT

Colo. Plateau uplifted;

Streams, Colo. River vigorously downcut through Plateau

WHEN

Late Tertiary/Early Quaternary (~15 - 5 mya)

~5 mya to present

PRODUCT

Softer Mesozoic sediments stripped off harder surface of Kaibab Limestone

Deep canyons expose one of greatest pC/Paleozoic rock sequences in world

Vishnu Schist

Tapeats Sandstone

Bright Angel Shale

Great Unconformity

Zion National Park and vicinity: younger (Mesozoic) rocks that overlie Grand Canyon sequence-- mostly cross-bedded sandstones

Most of Colo. Plateau (except higher elevations) is desert

Contains elements of the 4 major desert types

Region experiences summer monsoons

Colorado Plateau’s mean elevation = 5200 ft. (1730 m); range = 3000 - 14,000 ft. (1000 - 4670 m)

High elevation + deep canyons => huge elevational/ climatic gradients

Merriam developed life zone concept on the Colorado Plateau:

80 miles (130 km) apart

Lower Sonoran Zone, Inner Grand Canyon

Boreal Zone, San Francisco Peaks

A virtual hike down the Bright Angel Trail

On the South Rim: pinyon-juniper woodland

In mesic microsites on South Rim: Ponderosa pine

Drier woodland: mostly juniper

In mesic microclimates (north-facing slopes) below Rim: Douglas fir

Descending from Rim.....

On Tonto Plateau: Coleogyne (blackbrush) community

Hedgehog cactus Utah agave

Descending further......

Inner Canyon: Sonoran desert

Mesquite tree

Sacred Datura Barrel cactus

More mesic (heavy winter snowfall)

Ponderosa pine, aspen, spruce, fir

North Rim and North Kaibab National Forest

Mojave Desert (west/SW of Colorado Plateau)

Creosotebush

Desert tortoise

A quick tour of some Colorado Plateau fauna

Desert bighorn sheep

Mule deer

Canyon wrens

Wild turkey

Chuckwalla

Horned toad

Collared lizard

Grand Canyon rattlesnake

Humans at Grand Canyon and vicinity

10,000 years ago : Paleoindians at Grand Canyon

3000-4,000 years ago : Desert Culture at the Canyon

Split-twig figurine

500 - 1200 A.D. : Prehistoric Pueblo Peoples (Anasazi) in the Canyon (ancestors to modern Hopi)

Hilltop ruin, Cardenas Creek

Anasazi Bridge

1540 : First Europeans (Captain Garcia Lopez de Cardenas) visit Canyon with Hopi guides

1869 : Major John Wesley Powell leads first successful expedition down the Colorado River

Powell’s boat and armchair Tau-gu and

J.W. Powell

1871 : Mormon patriarch John D. Lee establishes Lee’s Ferry at Marble Canyon

1877 : John D. Lee executed for his role in 1857 Mountain Meadow massacre; Emma Lee (one of his many widows) runs ferry after his demise

1880 : 1st tourist facility (log cabin) built at South Rim

1883 : John Hance, first Grand Canyon settler, arrives

1889: C.H. Merriam explores Grand Canyon region, develops life zone concept

1908 : President Teddy Roosevelt creates Grand Canyon National Monument

1915 : Annual visitation to the Canyon reaches 106,000

1919 : Grand Canyon and Zion both become national parks

ca. 1920 : 1st mule trips for tourists into Grand Canyon

1922 : Phantom Ranch built at bottom of Grand Canyon (designed by architect Mary Jane Colter)

1938 : Elsie Clover and Lois Jotter conduct botanical survey as 1st women to float Grand Canyon on a commercial trip

1955 : Bill Beer and John Dagget swim entire length of Grand Canyon (Beer later writes book We Swam the Grand Canyon: The story of a cheap vacation that got a little out of hand)

1955 : Georgie White pioneers use of inflatable rafts in Grand Canyon; commercial river running takes off

1956 : Construction of Glen Canyon Dam is authorized

1963 : Gates of Glen Canyon Dam close, the Colorado River ceases to be a wild river through Grand Canyon

1964 : Bureau of Reclamation plans dam within Grand Canyon; Sierra Club leads successful fight against it

1983 : Record spring runoff in Colorado River basin causes flood that nearly takes out Glen Canyon Dam:

Sheets of plywood extend height of dam 4 ft., enough to prevent water from over-topping dam3 dory boatmen on illegal trip set unmotorized speed record: 277 miles in 3 days

1989 : Congress requires operators of Glen Canyon Dam to assess dam operations and ways to minimize impacts to the Grand Canyon

1993 : Suicides (leaping/driving off Rim) at Grand Canyon soar following release of movie Thelma and Louise

1996 : 1st captivity-bred California condors released into wild near Marble Canyon

2004 : 1st PEL Semi-occasional Phytogeographic and Hiking Expedition to Grand Canyon area

Acknowledgements

Thanks to Bob Ribokas’ excellent website,

www.kaibab.org

...and to many other websites from which I stole, I mean borrowed images