Natural Resources
Conservation Service
Ecological site R030XC380AZ
Sandy Loam Upland
13-17" p.z.
Cobbly Surface
Accessed: 08/25/2026
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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.
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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): 030X–Mojave Basin and Range
AZ CRA 30.3 – Upper Mohave Desert
Elevations range from 2800 to 4500 feet and precipitation averages 9 to 12 inches per year. Vegetation includes Joshua tree, blackbrush, creosotebush, ratany, bush muhly, big galleta, black grama, desert needlegrass, and Indian ricegrass. The soil temperature regime is thermic and the soil moisture regime is typic aridic. This unit occurs within the Basin and Range Province and is characterized by broad basins, valleys, and old lakebeds. Widely spaced mountains trending north to south occur throughout the area. Isolated, short mountain ranges are separated by an aggraded desert plain. The mountains are fault blocks that have been tilted up. Long alluvial fans coalesce with dry lakebeds between some of the ranges.Associated sites
R030XC318AZ Sandy Loam Upland 10-13" p.z. Limy, Skeletal
R030XC381AZ Limestone/Sandstone Cliffs 13-17" p.z.
Table 1. Dominant plant species
Tree (1) Juniperus osteosperma
Shrub (1) Coleogyne ramosissima
(2) Quercus turbinellaHerbaceous Not specified
Physiographic features
This site occurs on summits and shoulders of fan terraces. The soil associated with this site is very cobbly throughout the profile.
Table 2. Representative physiographic features
Landforms (1) Fan
(2) Terrace
Flooding frequency None Ponding frequency None Elevation 4300 – 6500 ft Slope 5 – 15 % Aspect Aspect is not a significant factor Climatic features
Precipitation in this LRU ranges from 13-17 inches. Winter-summer rainfall ratios range from 70-30% to 60-40%. Snowfall is common throughout the area and ranges from a trace to 10 inches. At the lower elevations, snow seldom persists more than a day. Summer rains fall July-September, originate in the Gulf of Mexico, and are convective thunderstorms. Winter moisture is frontal, originates in the northern Pacific, and falls as rain or snow in widespread storms of low intensity and long duration. May and June are the driest months of the year. Humidity is generally low. Temperatures are warm in the summer and cold in the winter. Freezing temperatures are common October-May. Winter-summer rainfall ratios in this LRU average 65% to 35%.
Table 3 Representative climatic features
Frost-free period (average) 230 days Freeze-free period (average) 300 days Precipitation total (average) 20 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
The soil of this site is deep and very cobbly throughout the profile.
A typical profile is:
0-2 inches - brown, very cobbly sandy loam
2-6 inches - brown, very cobbly loam
6-37 inches - reddish yellow, very cobbly clay loam
37-45 inches - yellowish red, very cobbly sandy clay loam
45-60 inches - white, weakly lime cemented, very cobbly sandy loam.
Depth to bedrock ranges from 40 to 60 inches.
Soils correlated to this ecological site include 623081, Tsezhin very cobbly sandy loam, Shivwits Area, Arizona, Part of Mohave County Soil Survey Area.Table 4. Representative soil features
Surface texture (1) Very cobbly sandy loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately slow Soil depth 40 – 60 in Surface fragment cover <=3" 25 % Surface fragment cover >3" 25 % Available water capacity
(0-40in)4.2 – 8.3 in Calcium carbonate equivalent
(0-40in)0 – 5 % Electrical conductivity
(0-40in)0 – 2 mmhos/cm Sodium adsorption ratio
(0-40in)Not specified Soil reaction (1:1 water)
(0-40in)7.4 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)25 % Subsurface fragment volume >3"
(Depth not specified)25 % Ecological dynamics
The historic climax plant community (HCPC) for a site in North America is the plant community that existed at the time of European immigration and settlement. It is the plant community that was best adapted to the unique combination of environmental factors associated with the site. The historic climax plant community was in dynamic equilibrium with its environment. It is the plant community that was able to avoid displacement by the suite of disturbances and disturbance patterns (magnitude and frequency) that naturally occurred within the area occupied by the site. Natural disturbances, such as drought, fire, grazing by native fauna, and insects, were inherent in the development and maintenance of these plant communities. The effects of these disturbances are part of the range of characteristics of the site that contribute to that dynamic equilibrium. Fluctuations in plant community structure and function caused by the effects of these natural disturbances establish the boundaries of dynamic equilibrium. They are accounted for as part of the range of characteristics for an ecological site. Some sites may have a small range of variation, while others have a large range.
The historic climax plant community of an ecological site is not a precise assemblage of species for which the proportions are the same from place to place or from year to year. In all plant communities, variability is apparent in productivity and occurrence of individual species. Spatial boundaries of the communities; however, can be recognized by characteristic patterns of species composition, association, and community structure. The HCPC for this ecological site has been estimated by sampling relict or relatively undisturbed sites and/or reviewing historic records.
Plant communities that are subjected to abnormal disturbances and physical site deterioration or that are protected from natural influences, such as fire and grazing, for long periods seldom typify the historic climax plant community. The physical site deterioration caused by the abnormal disturbance results in the crossing of a threshold or irreversible boundary to another state, or equilibrium, for the ecological site. There may be multiple thresholds and states possible for an ecological site, determined by the type and or severity of abnormal disturbance. The known states and transition pathways for this ecological site are described in the accompanying state and transition model.
The Plant Community Plant Species Composition table provides a list of species and each species or group of species’ annual production in pounds per acre (air-dry weight) expected in a normal rainfall year. Low and high production yields represent the modal range of variability for that species or group of species across the extent of the ecological site.
The Annual Production by Plant Type table provides the median air-dry production and the fluctuations to be expected during favorable, normal, and unfavorable years.
The present plant community on an ecological site can be compared to the various common vegetation states that can exist on the site. The degree of similarity is expressed through a similarity index. To determine the similarity index, compare the production of each species to that shown in the plant community description. For each species, count no more than the maximum amount shown for the species, and for each group, count no more than the maximum shown for the group. Divide the resulting total by the total representative value shown in the Annual Production by Plant Type table for the reference plant community. Variations in production due to above or below normal rainfall, incomplete growing season or utilization must be corrected before comparing it to the site description. The Worksheet for Determining Similarity Index is useful in making these corrections. The accompanying growth curve can be used as a guide for estimating percent of growth completed.
State and transition model
Custom diagramStandard diagram
More interactive model formats are also available. View Interactive Models
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 1
Historic Climax Plant CommunityCommunity 1.1
Historic Climax Plant CommunityThe aspect of this plant community is blackbrush mixed with chaparral shrubs and scattered trees with a limited understory of mixed grasses and forbs. In addition to blackbrush, turbinella oak, manzanita and desert ceanothus are common shrub species.
In the abscense of fire or other disturbance the plant community trends towards towards one with a substantial amount of pinyon and juniper trees, especially at higher elevations.
Immediately after disturbance from fire or other vehicle the plant community will be dominated by annual grasses, forbs and half shrubs, including red brome and/or cheatgrass and broom snakeweed. Yerba santa will be one of the earliest shrub species to increase. Within 5 to 10 years chaparral shrub species, such as turbinella oak, desert ceanothus and manzanita, will begin to reestablish in substantial amounts. If not disturbed again the plant community will return to a mix of trees, shrubs, forbs and grasses with trees again a major component of the plant community, especially at higher elevations. Blackbrush will not be a major component of this new plant community. It will take tens or hundreds of years for blackbrush to return to predisturbance levels, if it does at all.Figure 4. Annual production by plant type (representative values) or group (midpoint values)
Table 5. Annual production by plant type
Plant type Low
(lb/acre)Representative value
(lb/acre)High
(lb/acre)Shrub/Vine 558 638 716 Tree 108 161 215 Forb 26 39 52 Grass/Grasslike 8 12 17 Total 700 850 1000 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Occasional Native Annual Grasses 8–17 sixweeks fescue VUOC Vulpia octoflora 8–17 – Forb2 Occasional Native Perennial Forbs 8–17 Forb, perennial 2FP Forb, perennial 0–8 – rockcress ARABI2 Arabis 0–8 – winding mariposa lily CAFL Calochortus flexuosus 0–8 – beardtongue PENST Penstemon 0–8 – 3 Occasional Native Annual Forbs 17–34 Forb, annual 2FA Forb, annual 17–34 – Shrub/Vine4 Dominant Native Shrubs 382–425 blackbrush CORA Coleogyne ramosissima 382–425 – 5 Common Native Shrubs 136–230 Sonoran scrub oak QUTU2 Quercus turbinella 85–128 – manzanita ARCTO3 Arctostaphylos 42–60 – desert ceanothus CEGR Ceanothus greggii 8–42 – 6 Occasional Native Shrubs 42–85 Nevada jointfir EPNE Ephedra nevadensis 0–8 – mormon tea EPVI Ephedra viridis 0–8 – Eastern Mojave buckwheat ERFAP Eriogonum fasciculatum var. polifolium 0–8 – yerba santa ERIOD Eriodictyon 0–8 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–8 – desert almond PRFA Prunus fasciculata 0–8 – Mexican cliffrose PUME Purshia mexicana 0–8 – turpentinebroom THMO Thamnosma montana 0–8 – 7 Occasional Native Cacti 0–8 pricklypear OPUNT Opuntia 0–8 – 8 Occasional Native Agave-Yucca-Likes 0–8 banana yucca YUBA Yucca baccata 0–8 – Tree9 Common Native Trees 85–170 Utah juniper JUOS Juniperus osteosperma 85–170 – 10 Occasional Native Trees 26–42 singleleaf pinyon PIMO Pinus monophylla 26–42 – Interpretations
Animal community
Steep side slopes into drainages limit livestock movement.
The site provides crucial summer habitat for mule deer.
Potential wildlife species include scrub jay, bushtit, long-eared owl, ash-throated flycatcher, rufours-sided towhee, American kestrel, mule deer, coyote, woodrat, brush mouse, great basin pocket mouse, cottontail, gray fox, cougar, striped whiptail, short-horned lizard, gopher snake, striped whipsnake, great basin rattlesnake.Recreational uses
The site is used for hunting and wildlife observation.
Supporting information
Type locality
Location 1: Mohave County, AZ Township/Range/Section T37 N. R16 W. S20 General legal description Arizona, Mohave Co., Virgin Peak, NV - AZ 7 1/2 min. quad., Sec. 20, T. 37 N., R. 16 W. Contributors
Larry D. Ellicott
Stephen Cassady
Steve CassadyRangeland health reference sheet
Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.
Author(s)/participant(s) Contact for lead author Date Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
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Presence of water flow patterns:
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Number and height of erosional pedestals or terracettes:
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Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
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Number of gullies and erosion associated with gullies:
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Extent of wind scoured, blowouts and/or depositional areas:
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Amount of litter movement (describe size and distance expected to travel):
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Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
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Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
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Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
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Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):
Dominant:
Sub-dominant:
Other:
Additional:
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Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
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Average percent litter cover (%) and depth ( in):
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Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
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Perennial plant reproductive capability:
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