Physiographic features

This site occurs on summits and upper sideslopes of fan remnants. Elevations are 2200 to 4730 feet. Slopes range from 2 to 8%.

Table 2. Representative physiographic features

Climatic features

The Mojave Desert experiences clear, dry conditions for a majority of the year. Winter temperatures are mild, summer temperatures are hot, and seasonal and diurnal temperature fluctuations are large. Monthly minimum temperature averages range from 30 to 80 degrees F (-1 to 27 degrees C). Monthly maximum temperature averages range from 60 to 110 degrees F (16 to 43 degrees C) (CSU 2002).

Average annual rainfall is between 2 and 8 inches (50 to 205 millimeters) (USDA 2006). Snowfall is more common at elevations above 4000 feet (1220 meters), but it may not occur every year (WRCC 2002b). The Mojave Desert receives precipitation from two sources. Precipitation falls primarily in the winter as a result of storms originating in the northern Pacific Ocean. The Sierra Nevada and Transverse Ranges create a rain shadow effect, causing little precipitation to reach the Mojave Desert. Sporadic rainfall occurs during the summer as a result of convection storms formed when moisture from the Gulf of Mexico or Gulf of California moves into the region. Summer rainfall is more common and has a greater influence on soil moisture in the eastern Mojave Desert.

Windy conditions are also common in the Mojave Desert, particularly in the west and central Mojave Desert. Spring is typically the windiest season, with winds averaging 10-15 miles per hour (WRCC 2002a). Winds in excess of 25 miles per hour and gusts in excess of 50 miles per hour are not uncommon (CSU 2002).

In the BLM Grazing Allotments Soil Survey (Northeast Part of Mojave Desert Area, CA (CA805)), most areas receive approximately 5 to 7 inches of precipitation annually (WRCC 2002b). At elevations above 4000 feet (1370 meters), average annual precipitation in the form of rain may reach 8 inches or more, and average annual snowfall may reach up to 10 inches (WRCC 2002b).

The data from the following climate stations were used to describe the climate in the BLM Grazing Allotments Soil Survey (station number in parentheses):
Pahrump, NV (265890)
Mountain Pass, CA (045890)
Searchlight, NV (267369)
Red Rock Canyon State Park, NV (266691)

"Maximum monthly precipitation" represents average monthly precipitation at Pahrump, NV.

Table 3. Representative climatic features

Influencing water features

Soil features

The soils associated with this site are very deep and well drained. They are formed on stable, older alluvial surfaces from mixed alluvium or alluvium derived from limestone. Soils are sandy or coarse-loamy throughout. The soils are moderately to strongly alkaline throughout. Available water holding capacity is low and permeability is slow to moderately rapid. Soils classify as sandy, mixed, thermic Duric Torriorthents (Spider series) or coarse-loamy, mixed, thermic Typic Haplocalcids (Weiser series).

These soils are found on stable, older alluvial soils. The stability and are of these landforms allows for the development of silica-cemented nodules (Spider soils) and/or horizons high in calcium carbonate in soils formed from limestone parent materials (Weiser soils).

This ecological site is found in the following Map units and soil components:

SSA Map unit Component

CA697 - 155 - Spider
CA697 - 251 - Spider

CA805 - 3650 - Weiser

Table 4. Representative soil features

Animal community

WILDLIFE COMMUNITIES (Brown and Nagy 1995; Brydolf 1996; Recht 1995):

a. This site provides suitable habitat for mammals such as antelope ground squirrels; pocket mice; Merriam's and Great Basin kangaroo rats; and black-tailed jackrabbits and coyotes. Shadscale seeds are used by several species of small mammals. The twigs and foliage provide forage for jackrabbits and some small mammals.

b. This site provides habitat for lizards such as the western whiptail; side-blotched lizard and desert horned lizard. The sandy subsurface textures may be a limiting factor for burrowing reptiles such as desert tortoise.

c. Birds common to this site include common ravens, black-throated and sage sparrows, and rock wrens.

Wildlife Habitat:

Management for this site would be to protect it from excessive disturbance and maintain existing plant cover. Close roads and trails no longer being used and revegetate using native species indigenous to this site. Vehicle activity off of designated roads and tank trails can result in destruction of desert tortoise and small mammal burrows. Water developments would increase the species diversity of this site.


Livestock grazing:

a. Season of Use- Other Mgt. Considerations: Shadscale is considered valuable browse for cattle and sheep. Shadscale is often eaten during the early spring before spines mature. The seeds are also readily eaten by livestock. White bursage is fair browse for cattle and horses, and fair to good browse for goats. Sheep also use this shrub, feeding primarily on new growth and seeds. Creosotebush is unpalatable to livestock. Domestic sheep use creosotebush primarily for shade. During favorable years, perennial and annual forbs and grasses provide additional forage.

b. General guide to initial stocking rate. Before making specific recommendations, an on-site evaluation must be made.

Hydrological functions

Runoff is low. Hydrologic soil group A - soils having high infiltration rates even when thoroughly wetted and consisting chiefly of deep, well drained to excessively drained sands or gravels. Hydrologic conditions: good - >70% ground cover (includes litter, grass and brush overstory); fair - 30 to 70% ground cover; poor <30% ground cover.

Soil Series: Spider

Hydrologic Group: A

Hydrologic Conditions and Runoff Curves:

Good:49
Fair: 55
Poor: 63

Recreational uses

This site is highly valued for open space and those interested in desert ecology. Flowering wildflowers and shrubs may also attract visitors during the spring.

Other information

Revegetation of Disturbed Areas:

Species indigenous to this site are recommended for any revegetation efforts. Shadscale, white bursage and creosotebush are effective shrubs for revegetation of disturbed sites. Transplanting seedlings is more effective than direct seeding. Planting in late fall or early spring allows for acclimation to summer conditions. Transplants that are dormant during the hot, dry season are best maintained that way rather than attempting to force them to break dormancy and undergo new vegetative growth out of season. Supplemental irrigation is recommended for the first growing season, especially if winter rainfall has been sparse. Protection from rodents is also recommended.

Military Operations:

Management for this site would be to protect it from excessive disturbance and maintain existing plant cover. Land clearing or other disturbances that destroy the vegetation and the soil crust and structure can result in soil compaction, reduced infiltration rates, accelerated erosion, soil blowing and barren areas. The frequency of flash flooding may also increase with increased surface runoff and loss of vegetative cover. Rest or protect sites from further disturbance. Deep ripping heavily compacted soil facilitates water infiltration, seed germination, rapid root growth and improves overall plant survival and growth. Gully stabilization methods include straw bale checkdams, rock riprap, and sand bags.

Inventory data references

NV-ECS-1
SCS-Range 417
Other form

Type locality

Other references

Brown, T.K. and K. A. Nagy with R.D. Nieuhaus,Inc. 1995. Final Report, Herpetological Surveys and Physiological Studies on the Western Portion of Fort Irwin NTC.

Brydolf, B. with R.D. Nieuhaus, Inc. 1996. Final Report, 1994 Avian Survey at the National Training Center, Fort Irwin, CA.

Recht, M.A. with R.D. Nieuhaus, Inc. 1995. Final Report, 1994 Small Mammal Surveys of Selected Sites at the National Training Center Fort Irwin, California.

Contributors

P. Novak-Echenique, Allison Tokunaga

Approval

Sarah Quistberg, 2/26/2025