Natural Resources
Conservation Service
Ecological site R040XD004CA
Hyper-Arid Hill 2-4" p.z.
Last updated: 2/08/2019
Accessed: 11/13/2024
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.
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).
XD LRU concept:
The XD LRU is an extremely hot and dry portion of the MLRA. Mean annual precipitation is about 4 inches or less where the majority of the precipitation can arrive in only a couple storm events during any given year. The very few hard freezing days allows this region to have Plant Hardiness Zones of 9b or warmer. This LRU covers most of the Lower Colorado Desert except elevations above 500 m where Plant Hardiness Zones are less than 9b.
Classification relationships
Mojave Creosote Bush (Holland, 1986).
Larrea tridentata Shrubland Alliance (Sawyer et al. 2009).
Ecological site concept
This ecological site occurs on sideslopes of fan remnants and hills at elevations of 460 to 1800 feet. Soils are typically very deep but may be moderately deep over a duripan, or very shallow over bedrock on hills. The most important abiotic factors driving this site are a very dry climate with hyperthermic soil temperatures, steep slopes and rocky soils with low moisture holding capacity.
Production reference value (RV) is 75 pounds per acre with a range from 25 to 125 pounds per acre. The extreme aridity of this site restricts the potential vegetation to a very sparse, widely spaced creosote bush community with annual forbs contributing 50 to 80 percent of annual production during average to above average precipitation conditions.
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 map unit or greater).
This description was copied from and is equivalent to R031XY004CA. There is ongoing LRU concept development and designation where a request was made by the Region 8 Ecological Site Specialist to avoid using the default XY LRU.
Associated sites
R040XD015CA |
Limy 4-6" p.z. This ecological site is on fan aprons and fan remnants with creosote bush and burrobush. |
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R040XD017CA |
Steep Granitic Slope 4-6" p.z. This ecological site occurs on hills with burrobush, teddybear cholla, creosote bush, and a mix of other species. |
R040XD021CA |
Very Gravelly Wash This small ephemeral stream occurs on interfluves and inset fans among desert pavement surfaces. |
R040XD001CA |
Limy Hill 4-6" p.z. This ecological site is on north facing hills and sideslopes of fan remnants. Burrobush and creosote bush dominate. |
R040XD010CA |
Valley Wash This ephemeral stream occurs in the broad drainageways with large frequent flood events. Desert willow and blue paloverde are present. |
Similar sites
R030XD004CA |
Low-Production Hyperthermic Hills This ecological site is similar but occurs in the Mojave Desert and has higher production. |
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R040XD001CA |
Limy Hill 4-6" p.z. This site is higher producing with a significant burrobush component. This site is typically found on north-facing slopes. |
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
(1) Larrea tridentata |
Herbaceous |
(1) Plantago ovata |
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