

Natural Resources
Conservation Service
Ecological site R030XC238CA
Bi-Modal Semi-Desert Deep Fans 8-10 inches
Last updated: 2/25/2025
Accessed: 03/15/2025
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
MLRA notes
Major Land Resource Area (MLRA): 030X–Mojave Basin and Range
MLRA Description:
Major Land Resource Area (MLRA) 30, Mojave Desert, is found in southern California, southern Nevada, the extreme southwest corner of Utah and northwestern Arizona within the Basin and Range Province of the Intermontane Plateaus. Elevations within the MLRA range from basin floors below sea level to mountains over 12,000 feet (3650 meters) high. The climate of the area is hot and dry with mostly hyperthermic and thermic soil temperature regimes and aridic soil moisture regimes. However, at higher elevations of this MLRA, generally above 5,000 feet, soil temperature regimes can be mesic, cryic and frigid with xeric soil moisture regimes. Due to the extreme elevational range found within this MLRA, land resource units (LRUs) were designated to group the MLRA into similar land units.
LRU Description:
The Bi-Modal Semi-Arid (XC) Land Resource Unit (LRU), represents a semi-arid zone as defined by the United Nations Food and Agriculture Organization and is a semi-arid region distinguished by other semi-arid regions of the Mojave by the amounts of summer precipitation it receives. Semi-arid regions in the western Mojave can experience hot and very dry summers whereas regions within the XC LRU can receive more than 2.5 inches (63.5 mm) of rain during the months of July, August and September. The Bi-Modal Semi-Arid LRU is found primarily in eastern Mojave such as in Nevada at the higher elevations, in California in the New York, Providence, Castle and Clark Mountain Ranges as well as the Cerbat and Virgin Mountains of Arizona. Elevations range from approximately 4000 to 12,000 feet (1500 to 3650 meters) and precipitation ranges 8 to 18 inches (200 – 450 mm) per year in the form of rain. Snow is not uncommon in this LRU with the chance of receiving 3 to 48 inches of snow per year.
Due to the relatively high volume of summer rainfall, soil moisture regimes may have been designated as ustic-aridic, however emerging soil moisture data suggests the xeric-aridic soil moisture regime may be more appropriate and is likely to dominate this LRU. Soils within this LRU also have a cool thermic or cooler soil temperature regime. The combination of cooler temperatures [mean annual air temperatures lower than 62 degrees F (17 degrees C)] with summer monsoonal rains help to create a unique climate within the Mojave Desert which may be more similar to the Southern Nevada Basin and Range (MLRA). Vegetation at the lower elevations of this LRU includes blackbrush, Joshua tree, juniper, pinyon pine, and mountain big sagebrush. At the higher elevations, vegetation includes oaks, Mojave sagebrush, Ponderosa pine, white fir, limber pine and the Great Basin bristlecone pine.
Classification relationships
Class - 3 Xeromorphic Woodland, Scrub & Herb Vegetation Class
Subclass - 3.B Cool Semi-Desert Scrub & Grassland Subclass
Formation - 3.B.1 Cool Semi-Desert Scrub & Grassland Formation
Division - 3.B.1.Ne Western North American Cool Semi-Desert Scrub & Grassland Division
Macrogroup - 3.B.1.Ne.1 Chrysothamnus viscidiflorus - Coleogyne ramosissima / Achnatherum hymenoides Great Basin & Intermountain Dry Shrubland & Grassland Macrogroup
Group - 3.B.1.Ne.1.a Yucca brevifolia - Eriogonum fasciculatum - Ephedra fasciculata Mixed Desert Scrub Group
Alliance - 3.B.1.Ne.1.a Coleogyne ramosissima Mojave Desert Shrubland Alliance
(Schulz 2014)
Ecological site concept
This ecological site occurs on fan remnants and fan aprons and the concave areas within these landforms (inset fans) in the upper fan piedmont. Soils have a xeric-aridic soil moisture regime (sometimes designated as ustic-aridic), and a cool thermic soil temperature regime. Soils are very deep, with a sandy particle size control section. This site receives additional run-on from adjacent mountains. The reference plant community is dominated by blackbrush (Coleogyne ramosissima). Joshua Tree (Yucca brevifolia var. jaegeriana) is an emergent canopy species at 1-3 percent cover. Surface flooding is generally not intense or frequent enough that it removes blackbrush, but can influence plant diversity. However, rare large flood events have the potential to alter the states and community phases of the ecological site.
This is a group concept and provisional STM that also covers the following ecological sites: R030XB014NV, R030XB090NV, R030XC001CA
Associated sites
R030XC007NV |
SHALLOW GRAVELLY LOAM 7-9 P.Z. R030XC007NV is found very close to the mountain fronts where soils are often very shallow to shallow to bedrock or a petrocalcic horizon. |
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R030XC232CA |
Petrocalcic Fan Remnants R030XC232CA soils are predominantly derived from alluvium from limestone and/or volcanic sources. |
R030XC236CA |
Lithic Slopes R030XC236CA is found on nearby low hills and ballenas with slopes generally greater than 15% slope. |
R030XY219CA |
Ustic Ephemeral Drainageway Order 3 R030XY219CA is an ephemeral wash with a Strahler stream order between 2 and 3. This ecological site drains the upper fan piedmont areas and landforms with an ustic-aridic soil moisture regime. |
R030XY222CA |
Typic Aridic Ephemeral Drainageway Order 3 4-7" p.z. R030XY222CA is an ephemeral wash which typically drains landforms with a typic aridic (drier) soil moisture regime. Deep sandy soils at the lower elevations of map units with R030XC238CA often do not support the higher elevation species often found in R030XY219CA. |
Similar sites
R030XB014NV |
SHALLOW GRAVELLY LOAM 7-9 P.Z. R030XB014NV is a relic Range Site whose conceptual component has been included in Community Phase 2.1 of the R030XC238CA ecological site. |
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R030XB090NV |
GRAVELLY FAN 7-9 P.Z. R030XB090NV is a relic Range Site whose conceptual component has been included in Community Phase 2.1 of the R030XC238CA ecological site. |
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
(1) Coleogyne ramosissima |
Herbaceous |
Not specified |
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