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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): 040X–Sonoran Basin and Range
AZ 40.3 – Colorado Sonoran Desert
Elevations range from 300 to 1200 feet and precipitation averages 3 to 7 inches per year. Vegetation includes creosotebush, white bursage, brittlebush, Mormon tea, teddybear cholla, elephant tree, smoke tree, ocotillo, and big galleta. The soil temperature regime is hyperthermic and the soil moisture regime is typic aridic. This unit occurs within the Basin and Range Physiographic Province and is characterized by numerous mountain ranges that rise abruptly from broad, plain-like valleys and basins. Igneous and metamorphic rock classes dominate the mountain ranges and sediments filling the basins represent combinations of fluvial, lacustrine, colluvial and alluvial deposits.Table 1. Dominant plant species
Tree (1) Parkinsonia microphylla
Shrub (1) Ambrosia dumosa
(2) Larrea tridentata var. tridentataHerbaceous (1) Muhlenbergia porteri
(2) Pleuraphis rigidaPhysiographic features
This range site occurs in an upland position. It does not benefit from run-in moisture from adjacent areas. It does suffer loss from run-off. It is located on terraces and alluvial fans.
Table 2. Representative physiographic features
Landforms (1) Terrace
(2) Alluvial fan
Elevation 400 – 1000 ft Slope 0 – 6 % Climatic features
Precipitation in this common resource area ranges from 3-7 inches yearly. Despite historical averages in rainfall amounts, as one moves from east to west in this resource area rains become more unpredictable and variable with Coefficients of Variation of annual rainfall equal to 44% at Gila Bend and 65% at Mohawk. Winter-Summer rainfall ratios are 40-60%. Summer rains fall July-September, originate in the Gulf of Mexico and are convective, usually brief intense thunderstorms. Summer thunderstorms usually form over the mountains in the afternoon and spread to the valleys and plains in the evening. The intensity of this precipitation is moderate to heavy, but rarely lasts more than half an hour. Many times these storms produce little more than gusty winds and light showers. Cool season moisture tends to be frontal, originate in the Pacific and Gulf of California and falls in widespread storms with long duration and low intensity. Snow is very rare and falls normally only in the higher mountains.
Mean temperatures for the hottest month (Jul) is 93 F; the coldest month (Jan) is 53 F. Extreme temperatures of 125 F and 10 F have been recorded. Long periods with little or no effective moisture occur frequently.
The winter-spring precipitation is the most dependable on the site. Perennial grasses, though classed as warm season growers, grow actively year-round when moisture is available. Shrubs and trees generally respond to seasonal moisture. The two rainy periods bring about their respective production of either winter or summer annual grasses and forbs.Table 3 Representative climatic features
Frost-free period (average) 360 days Freeze-free period (average) 0 days Precipitation total (average) 10 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
Soils that are grouped together in this ecological site are shallow to plant root restricting layers. Surface soil texture has a depth of 2-5 inches and range in texture from sand, gravelly loam to clay. Underlying layers have moderately slow to rapid permeability rates, but can absorb and hold all the moisture the climate supplies. Soluble salt accumulations are low. pH ranges from 7.9-8.4. With good vegetation cover, infiltration rates are high to moderate. Stability against erosion processes is good and plant-soil moisture relationships are very good. Coarse fragments may occur throughout the soil.
Soils mapped on this site include: in SSA-627 Southern Mohave county MU's Cherioni-28 & Cipriano-31; SSA-645 Aguila-Carefree area MU's Cipriano-69 & 107; SSA-653 Gila Bend-Ajo area MU's Cherioni CoXFSL-8, Cherioni GrXL-8 & Cavelt-39.Table 4. Representative soil features
Parent material (1) Alluvium – volcanic breccia
Surface texture (1) Gravelly sandy loam
(2) Very gravelly fine sandy loam
(3) Extremely gravelly loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately rapid to rapid Soil depth 4 – 20 in Surface fragment cover <=3" 20 – 60 % Surface fragment cover >3" 1 – 5 % Available water capacity
(0-40in)0.24 – 2 in Calcium carbonate equivalent
(0-40in)10 – 35 % Electrical conductivity
(0-40in)0 – 2 mmhos/cm Sodium adsorption ratio
(0-40in)Not specified Soil reaction (1:1 water)
(0-40in)7.9 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)20 – 60 % Subsurface fragment volume >3"
(Depth not specified)1 – 5 % Ecological dynamics
The plant communities found on an ecological site are naturally variable. Composition and production will vary with yearly conditions, location, aspect, and the natural variability of the soils. The Historical Climax Plant Community represents the natural potential plant communities found on relict or relatively undisturbed sites. Other plant communities described here represent plant communities that are known to occur when the site is disturbed by factors such as fire, grazing, or drought.
Production data provided in this site description is standardized to air dry weight at the end of the summer growing season. The plant communities described in this site description are based on near normal rainfall years.
NRCS uses a Similarity Index to compare existing plant communities to the plant communities described here. Similarity index is determined by comparing the production and composition of a plant community to the production and composition of a plant community described in this site description. To determine Similarity index, compare the production (air dry weight) 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 amount shown for each group. Divide the resulting total by the total normal year production shown in the plant community description. If the rainfall has been significantly above or below normal, use the total production shown for above or below normal years. If field data is not collected at the end of the summer growing season, then the field data must be corrected to the end of the year production before comparing it to the site description. The growth curve can be used as a guide for estimating production at the end of the summer growing season.
State and transition model
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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 plant community is predominantly desert shrubs and cacti with creosotebush dominant on the site. Perennial grass cover is sparse and annual grasses and forbs make up a small percentage of the community.
As palatable forage production on this site is very low, the plant community has changed very little, from potential, since the introduction of domestic grazing.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 85 90 95 Tree 1 5 10 Grass/Grasslike 5 7 10 Forb 1 3 5 Total 92 105 120 Figure 5. Plant community growth curve (percent production by month). AZ4041 , 40.3 3-7" p.z. all sites. Most growth occurs in the winter to early spring, plants are dormant May through October..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 5 20 40 25 0 0 0 0 0 0 5 5 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Perennial Grasses 5–10 threeawn ARIST Aristida 0–1 – low woollygrass DAPU7 Dasyochloa pulchella 0–1 – bush muhly MUPO2 Muhlenbergia porteri 0–1 – big galleta PLRI3 Pleuraphis rigida 0–1 – 2 Annual Grasses 1–5 sixweeks threeawn ARAD Aristida adscensionis 0–1 – needle grama BOAR Bouteloua aristidoides 0–1 – sixweeks grama BOBA2 Bouteloua barbata 0–1 – sixweeks fescue VUOC Vulpia octoflora 0–1 – Forb3 Forbs 0–5 trailing windmills ALIN Allionia incarnata 0–1 – common fiddleneck AMMEI2 Amsinckia menziesii var. intermedia 0–1 – New Mexico silverbush ARNE2 Argythamnia neomexicana 0–1 – smallflowered milkvetch ASNU4 Astragalus nuttallianus 0–1 – milkvetch ASTRA Astragalus 0–1 – desert marigold BAMU Baileya multiradiata 0–1 – California suncup CACA32 Camissonia californica 0–1 – brittle spineflower CHBR Chorizanthe brevicornu 0–1 – devil's spineflower CHRI Chorizanthe rigida 0–1 – Esteve's pincushion CHST Chaenactis stevioides 0–1 – cryptantha CRYPT Cryptantha 0–1 – hairy prairie clover DAMO Dalea mollis 0–1 – flatcrown buckwheat ERDE6 Eriogonum deflexum 0–1 – miniature woollystar ERDI2 Eriastrum diffusum 0–1 – desert trumpet ERIN4 Eriogonum inflatum 0–1 – buckwheat ERIOG Eriogonum 0–1 – little deserttrumpet ERTR8 Eriogonum trichopes 0–1 – spurge EUPHO Euphorbia 0–1 – California fagonbush FALA Fagonia laevis 0–1 – gilia GILIA Gilia 0–1 – desert lily HEUN2 Hesperocallis undulata 0–1 – Gordon's bladderpod LEGO Lesquerella gordonii 0–1 – pepperweed LEPID Lepidium 0–1 – foothill deervetch LOHU2 Lotus humistratus 0–1 – strigose bird's-foot trefoil LOSTT Lotus strigosus var. tomentellus 0–1 – Coulter's lupine LUSP2 Lupinus sparsiflorus 0–1 – Parry's false prairie-clover MAPA7 Marina parryi 0–1 – bristly nama NAHI Nama hispidum 0–1 – glandular threadplant NEGL Nemacladus glanduliferus 0–1 – evening primrose OENOT Oenothera 0–1 – combseed PECTO Pectocarya 0–1 – desert Indianwheat PLOV Plantago ovata 0–1 – Coues' cassia SECO10 Senna covesii 0–1 – dwarf blue-eyed grass SIMI2 Sisyrinchium minus 0–1 – desert globemallow SPAM2 Sphaeralcea ambigua 0–1 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 0–1 – woollyhead neststraw STMI2 Stylocline micropoides 0–1 – woolly tidestromia TILA2 Tidestromia lanuginosa 0–1 – Shrub/Vine4 Dominant Shrubs 30–85 burrobush AMDU2 Ambrosia dumosa 15–40 – creosote bush LATRT Larrea tridentata var. tridentata 15–40 – ocotillo FOSP2 Fouquieria splendens 5–15 – white ratany KRGR Krameria grayi 5–15 – 5 Misc. Shrubs 5–10 burrobush AMDU2 Ambrosia dumosa 15–40 – triangle bur ragweed AMDE4 Ambrosia deltoidea 1–3 – San Felipe dogweed ADPO Adenophyllum porophylloides 0–1 – brittlebush ENFA Encelia farinosa 0–1 – littleleaf ratany KRER Krameria erecta 0–1 – desert-thorn LYCIU Lycium 0–1 – desert ironwood OLTE Olneya tesota 0–1 – woody crinklemat TICAC Tiquilia canescens var. canescens 0–1 – American threefold TRCA8 Trixis californica 0–1 – 6 Succulents 10–15 buckhorn cholla CYACA2 Cylindropuntia acanthocarpa var. acanthocarpa 0–1 – Arizona pencil cholla CYAR14 Cylindropuntia arbuscula 0–1 – teddybear cholla CYBI9 Cylindropuntia bigelovii 0–1 – Wiggins' cholla CYEC3 Cylindropuntia echinocarpa 0–1 – Christmas cactus CYLE8 Cylindropuntia leptocaulis 0–1 – branched pencil cholla CYRA9 Cylindropuntia ramosissima 0–1 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 0–1 – candy barrelcactus FEWI Ferocactus wislizeni 0–1 – globe cactus MAMMI Mammillaria 0–1 – beavertail pricklypear OPBA2 Opuntia basilaris 0–1 – Tree7 Tree 1–10 ocotillo FOSP2 Fouquieria splendens 5–15 – yellow paloverde PAMI5 Parkinsonia microphylla 1–10 – Interpretations
Animal community
Within many large areas of this site are inclusions of better range sites (sand bottoms, loamy bottoms, sandy loam upland). In these instances, the entire area should be managed for the inclusions as they are producing nearly all the forage.
Forage production on this site is very low and management designed to maintain or improve the better sites associated with and adjacent to will benefit this site.
Wildlife found on this site are usually in transit to or from adjacent sites used for food and cover.Recreational uses
Landform includes terraces, fans, and bajadas located at the base of desert mountains. These areas have a sparse cover of desert shrubs and cacti, with plants so evenly spaced they have the appearance of being planted in a symmetrical pattern. Very few days in the fall, winter or spring are too uncomfortable to enjoy outdoor activities, however, summer heat (Jun-Aug) in the afternoon causes restrictions. Horseback riding, hiking and photography are activities to which this site is suited.
Other products
A few of these soils are mined for their gravel content.
Supporting information
Type locality
Location 1: La Paz County, AZ Township/Range/Section T1N R12W S2 General legal description Eagle Tail Ranch Contributors
Larry D. Ellicott
Steve Barker
UnknownRangeland 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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PrintThe Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.
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