Alan Barraza

University of Texas – El Paso

Los Pinos Mountains• Southern part of a mountain system

that extends northward along the Rio

Grande Rift.

• Uplifted during Laramide Orogeny

(40-70 Ma) and Rio Grande Rift

formation (25 –0 Ma)

• Pre-Cambrian age rocks (1.8 BA).

Composed of the Sias quartzite

(oldest), Blue Springs muscovite

schist (originally siltstones), White

Ridge quartzite, and Sevilleta rhyolite,

all intruded by the Los Pinos (pre-

Cambrian) granite. (Stark et al, 1946;

Luther et al., 2005)

Los Pinos Mountains

Soil Creation Process

• Regolith and soil can absorb and retain more water than bedrock

• Nutrients can be extracted easily compared to little to no extraction in bedrock

• Provides the environment needed for the most species of plants to grow.

Importance of Regolith and Soil

• Gain a general understanding of the following:

• landforms present in the eastern side of Los Pinos Mountains.

• processes occurring that are creating regolith and soil in the area

• abiotic factors affecting plant growth

Importance of Study

• Soil thickness will be correlated with landform, gradients of slopes, and aspect.

• Different landforms will entrap and incorporate dust at variable rates, given differences in landform morphology and age.

• This is because the source of the majority of soil material (i.e., clay, carbonate, silt) in analogous landforms elsewhere in semiarid slopes of NM is dust.

• Highest plant biomass and diversity will occur in the older Quaternary alluvial fill, given additional void space for soil water storage and higher soil water retention associated with clay and silt. Plant growth on the pediment will be influenced by thinner soil development. South and north facing slopes will be differently related to plant recruitment and productivity, primarily given soil differences associated with slope-controlled rates and processes of soil development.

Hypotheses

Mark out a 1meter x 1meter plot

Characterization of site:• GPS coordinates• Slope and aspect of the area• Qualitative description of the

surrounding area to include vegetation, clast size, and any other items of interest

• Photography of area

Transects• Create 2 diagonal transects across

the set plot• Every 10cm along each set

transect, identify and measure rocks directly on the transect line and under set mark

Field Methods

Soil Analyses

• Excavate a small hole (approximately 20cm x 20cm) until bedrock is reached.

• Collect a grab sample and run the soil through the soil sieve to remove all gravel and rocks.

• Analyze a dry soil ped for soil hardness

• Using 10% HCl, test the soil for any CaCO3.

• Analyze soil for wet consistency, plasticity, soil type identification using the ‘worm test’

• Measure depth of hole and approximate

vegetation coverage in plot

• Take note of root content

Field Methods (cont)

Silty Clay

Clay

Very Gritty

Very Gritty

Gritty

Velvety

Velvety and Sticky

Gritty and Sticky

Sand

Loamy Sand

Loamy Sand

Silt Loam

Silty Clay Loam

Extremely sticky and very smooth

Extremely sticky with slight grittiness

No

No

Yes

Yes

Yes (very stable)

Yes (very stable)

Yes (very stable)

Yes

Yes (very resistant to molding)

Yes (very resistant to molding)

No

No

Yes (dull surface; poorly formed)

Yes (dull surface; poorly formed)

Yes (shiny surface; well formed)

Yes (shiny surface; well formed)

yes (well formed; shiny surface)

yes (well formed; very shiny surface)

FirmFriable to

FirmFirm to

Extra Firm to

Extra

Loose

Loose

Soft

SoftSlightly

HardSlightly

Hard to Hard

Loose

Loose

Friable

FriableFriable to

Firm

Form Stable Ball Ribbon Out Moist Dry

Sandy loan GittyYes (easily deformed)

Yes (dull surface; poorly formed) Yes No

Very Friable Soft

Slightly Hard to HardHard to Very

HardHard to Very

Hard

Yes (very sticky)

Yes (very sticky)

Consistence:Ability to:

No

No

NoYes (slight to mod.)

Yes (slight to mod.)

YesYes (mod.)

Yes (mod.)

Yes (mod.)

Yes (strong)

Yes (strong)yes (well formed;

very shiny surface)

No

Yes (slight)

Yes

Yes

Yes

Yes

Yes

Yes

Field Criteria Used in Determining Major Textural Classes

Soil Textural Class Feel (moist) "Soils" Hands

Plastic Prop. Sticky

Yes

YesVery Gritty and Sticky

Clay Loam

Sandy Clay Loam

No

No

Yes (slight)Yes (slight to mod.)

Landform Plot # Veg Cover % Root Content Root Sizesmountain backslope 31 60 low finemountain backslope 49 30 mod finemountain footslope 51 20 low finemountain footslope 55 20 mod fine - med

intermediate alluvial terrance 15 50 high fine - lgolder alluvial fill 1 55 high fine - medolder alluvial fill 17 50 mod fineolder alluvial fill 39 75 low fineolder alluvial fill 53 5 very low small - med

youngest alluvial surface 20 0 mod fine - lgyoungest alluvial surface 37 50 mod fineyoungest alluvial surface 45 70 mod fine - lgyoungest alluvial surface 48 5 low small - lg

pediment backslope 7 15 low finepediment backslope 13 15 mod fine - medpediment backslope 26 40 low fine - medpediment footslope 11 5 high med- xlgpediment footslope 24 5 none nonepediment shoulder 41 15 low finepediment surface 3 20 low finepediment surface 5 25 low finepediment surface 9 0 very low finepediment surface 22 5 low fine

Landform Vs Plant Data (Exerpt)

Landform Plot # HCl Test Soil Color Soil Typemountain backslope 30 Neg 10YR 4/4 sandy clay loammountain backslope 32 Neg 10YR 4/4 sandy clay loammountain backslope 50 Neg 10YR 3/4 silt loammountain footslope 52 Neg 7.5YR 4/6 claymountain footslope 54 Neg 10YR 4/3 sandy clay loammountain summit 28 Neg 10YR 4/4 sandy clay loamolder alluvial fill 34 Neg 7.5YR 3/4 clayolder alluvial fill 36 Pos 7.5YR 5/4 silty clayolder alluvial fill 40 Neg 7.5YR 3/4 sandy clay loamolder alluvial fill 46 Neg 10YR 4/4 silty clay loam

younger alluvial surface 6 Neg 10YR 4/4 silty clay loamyounger alluvial surface 16 Pos 10YR 4/6 silty clayyounger alluvial surface 18 Neg 10YR 4/4 silty clayyounger alluvial surface 56 Pos 10YR 5/4 clay loam

pediment backslope 8 Neg 10YR 5/3 silt loampediment backslope 14 Pos 10YR 5/4 clay loampediment backslope 23 Pos 7.5YR 5/4 claypediment backslope 42 Neg 10YR 5/4 silt loampediment footslope 12 Neg 10YR 3/6 loampediment surface 4 Neg 10YR 5/4 silt loampediment surface 10 Neg 10YR 3/3 silt loampedimet shoulder 25 Neg 10YR 5/3 silty clay loam

Landform Vs Soil Data (exerpt)

• Very scattered results supports the idea of several processes taking place creating the various landforms.

• Closely correlated soil thickness and similar clast sizes on all pediment surfaces suggest that these landform are entrapping and incorporating dust at similar rates.

• Thicker soil and smaller clasts on alluvial surfaces demonstrate a different process taking place in the formation of these landforms.

• With a higher sampling size soil thickness versus slope gradient could possibly be highly correlated.

• Most plant data was very scattered. But, spatial distribution of piñon trees between older Quaternary alluvial fill and the pediment surface shows trees prefer the thinner soil. The majority of this soil is eolian dust thus could be better formed and better suited for plant recruitment.

Discussion

• Significant correlation between soil thickness and landform

• Approaching significant correlation between soil thickness and slope gradient.

• No significant correlation between soil thickness and azimuth

• Highest plant biomass did not occur on the older Quaternary alluvial fill, but instead on pediment surface. Plant biomass and soil thickness between pediment surface and slopes were not significantly different.

• Larger clast size does entrap more dust and this is apparent in the soil thicknesses of the various landforms except for the alluvial surfaces, and mountain summit which are undergoing different processes.

Conclusion

• What difference in the soil between the older Quaternary alluvial fill and the pediment surface is causing such a significant difference in piñon tree biomass?

• Where is the eolian dust forming?

• Why are do some species of plants dominate certain landforms?

• When where the various alluvial fills created?

Further Questions…

Questions????