Natural Resources
Conservation Service
Ecological site R040XD009CA
Gravelly Fan Remnants And Fan Aprons
Accessed: 11/02/2024
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.
Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
MLRA notes
Major Land Resource Area (MLRA): 040X–Sonoran Basin and Range
MLRA Description:
Major land resource area (MLRA) 31 is the Lower Colorado Desert. This area is in the extreme southeastern part of California, in areas along the Colorado River, and in Western Arizona. The area is comprised of rough, barren, steep, and strongly dissected mountain ranges, generally northwest to southwest trending that are separated by intermontane basins. Elevation ranges from approximately 275 feet below sea level at the lowest point in the Salton Trough to 2700 feet along low northwest to southeast trending mountain ranges. The average annual precipitation is 2 to 6 inches with high temporal and spatial variability. Winter temperatures are mild, summer temperatures are hot, and seasonal and diurnal temperature fluctuations are large. Monthly minimum temperature averages range from 40 to 80 degrees F (4 to 27 degrees C). Monthly maximum temperature averages range from 65 to 110 degrees F (18 to 43 degrees C) (WRCC 2002). Temperatures are rarely below 28 degrees F, and extremely rarely fall below 24 degrees F. Precipitation is bimodal, with approximately 20 to 40 percent of annual precipitation falling between July and September. This summer rainfall, in combination with very hot temperatures and very few to no days of hard freeze are what characterize this MLRA and distinguish it from the Mojave Desert (MLRA 30).
Ecological Site Concept -
This ecological site occurs on stable, broad fan remnants and fan aprons at elevations of 540 to 2620 feet. Soils are very deep with sandy and gravelly textures, a high cover of surface gravels and cobbles, and a high percentage of subsurface rock fragments (by volume).
Production reference value (RV) is 161 pounds per acre and depending on precipitation and annual forb production, ranges from 50 to 344 pounds per acre. Shrubs are widely spaced, and creosote bush (Larrea tridentata) and Schott’s dalea (Psorothamnus schottii) dominate the site. Deep soils and hyperthermic soil temperatures favor dominance by the deep-rooted creosote bush. Gravelly soils, and high surface rock fragment cover, which increases localized run-on and enhances habitat for Schott’s dalea.
Data ranges in the physiographic data, climate data, water features, and soil data sections of this Ecological Site Description are based on major components only (15 percent of mapunit or greater).
Classification relationships
This ecological site is found within the Larrea tridentata Shrubland Alliance (Sawyer et al. 2009).
Associated sites
R040XD001CA |
Limy Hill 4-6" p.z. R031XY001CA occurs on steep sideslopes of adjacent fan remnants. Creosote bush (Larrea tridentata) and burrobush (Ambrosia dumosa) dominate. |
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R040XD021CA |
Very Gravelly Wash R031XY021CA is found on adjacent small, occasionally flooded inset fans. Brittlebush (Encelia farinosa), creosote bush (Larrea tridentata), and big galleta (Pleuraphis rigida) are dominant species. |
R040XD030CA |
Extremely Stony Fan Remnants R031XY030CA occurs on adjacent extremely stony fan remnants. Teddybear cholla (Cylindropuntia bigelovii) and creosote bush (Larrea tridentata) are dominant species. |
R040XD034CA |
Gravelly, Braided, Ephemeral Stream R031XY034CA is found on adjacent occasionally flooded, braided ephemeral drainage systems. Desert lavender (Hyptis emoryi) and burrobrush (Hymenoclea salsola) are dominant species. |
Similar sites
R040XD030CA |
Extremely Stony Fan Remnants R031XY030CA occurs on fan remnants with stony surfaces. Production and shrub diversity are higher, and teddybear cholla (Cylindropuntia bigelovii) is an important species. |
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R040XD200CA |
Rarely Flooded Fans R031XY200CA is found on rarely flooded fan aprons and cobbly fan remnants. Production is higher, brittlebush (Encelia farinosa) is an important species, and Schott's dalea (Psorothamnus schottii) is trace if present. |
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
(1) Larrea tridentata |
Herbaceous |
(1) Chorizanthe brevicornu |
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