Natural Resources
Conservation Service
Ecological site R041XB201AZ
Breaks
8-12" p.z.
Last updated: 4/09/2021
Accessed: 08/19/2026
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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): 041X–Madrean Archipelago
AZ 41.2 – Chihuahuan – Sonoran Desert Shrubs
Elevations range from 2600 to 4000 feet and precipitation ranges from 8 to 12 inches per year. Vegetation includes mesquite, palo verde, catclaw acacia, soaptree yucca, creosotebush, whitethorn, staghorn cholla, desert saltbush, Mormon tea, burroweed, snakeweed, tobosa, black grama, threeawns, bush muhly, dropseed, and burrograss. The soil temperature regime is thermic 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.Associated sites
F041XB221AZ Loamy Bottom 8-12" p.z. woodland
F041XB222AZ Saline Bottom 8-12" p.z. woodland
R041XB206AZ Limy Fan 8-12" p.z.
Similar sites
R041XB219AZ Gypsum Upland 8-12" p.z.
Table 1. Dominant plant species
Tree Not specified
Shrub (1) larrea tridentata
(2) atriplex confertifoliaHerbaceous (1) Pleuraphis mutica
(2) aristidaPhysiographic features
This site occurs in the lowest elevations of the Madrean Basin and Range province in southeastern Arizona. It occurs on fan terraces, hill-slopes and ridge-tops formed in relict lacustrine (lake bed) sediments. The site is characterized by highly eroded, steep slopes and scarps intermingled with vegetated areas on more moderate slopes.
Table 2. Representative physiographic features
Landforms (1) Hill
(2) Fan remnant
(3) Scarp slope
Flooding frequency None Ponding frequency None Elevation 2600 – 4000 ft Slope 3 – 75 % Aspect N, E, S Climatic features
Precipitation ranges from 8-12 inches annually. More than half falls during July-Sep in brief, but often heavy, thunderstorms. The rest of the moisture comes as light rain or snow that falls slowly for a day or more, but rarely lasts more than a day. May and June are normally the driest months. Humidity is generally very low.
Temperatures are mild throughout most of the year. Freezing temperatures are common at night Dec-Feb; brief 0 F may be observed some nights. During June, July & August some days may exceed 100 F.
In years of average or greater winter precipitation, annual grasses and forbs occur abundantly in the interspaces.Table 3 Representative climatic features
Frost-free period (average) 240 days Freeze-free period (average) Precipitation total (average) BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
There are no water features associated with this site.
Soil features
These soils are well drained, variable in texture, stratified and saline and/or sodic. They have formed in old lacustrine deposits and may have strata of gypsum as well. Gypsum can be 5 to 20% by volume in the soil profile. They are not flooded.
Soil series mapped on this site include: SSA-662 Safford Area MU Ro Rough broken land; AZ-663 Gila-Duncan Area, Parts of Graham and Greenlee Counties MU's 6 torriorthents and calciorthids, 22 haplargids and torriorthents, and 26 orthents; SSA-664 San Simon Area, parts of Cochise, Graham, and Greenlee Counties MU 10 Calciorthids and torriorthents.Table 4. Representative soil features
Surface texture (1) Silt loam
(2) Fine sandy loam
(3) Clay loam
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Moderate to slow Soil depth 25 – 60 in Surface fragment cover <=3" 0 – 15 % Surface fragment cover >3" 0 – 5 % Available water capacity
(0-40in)2.5 – 6.2 in Calcium carbonate equivalent
(0-40in)1 – 15 % Electrical conductivity
(0-40in)0 – 4 mmhos/cm Sodium adsorption ratio
(0-40in)0 – 6 Soil reaction (1:1 water)
(0-40in)7.4 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)0 – 15 % Subsurface fragment volume >3"
(Depth not specified)0 – 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 community found on relict or relatively undisturbed areas of this site. Other plant communities described here represent plant communities that are known to occur when the site is disturbed by factors such as fire, grazing and 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 described in the 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 amount shown for that 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 the field data is not collected at the end of the summer growing season, then the field data must be corrected to the end of 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.
The historic native state includes the native plant communities that occur on the site, including the historic climax plant community. This state includes other plant communities that naturally occupy the site following fire, drought, flooding, herbivores and other natural disturbances. The historic climax plant community represents the natural climax community that eventually reoccupies the site with proper management and a return to near normal conditions and/or equilibrium.
State and transition model
Custom diagramStandard diagram
Figure 4. State and Transition, Breaks 8-12" p.z.
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 textState 1 submodel, plant communities
State 2 submodel, plant communities
State 1
Historic Climax Plant CommunityCommunity 1.1
Historic Climax Plant CommunityThis plant community is dominated by shrubs like creosote bush, shadscale, rayless goldenhead, white bursage, desert saltbush, fourwing saltbush and whitethorn acacia. Tobosa grass is a dominant plant in areas where clay lenses out-crop on the slopes. Annual grasses and forbs are an important part of the plant community. Cryptogams are common on this site, often completely colonizing outcrops of gypsum. The site is extremely susceptible to sheet, rill and gully erosion due to high concentrations of salts and soluble gypsum in the surface soil.
Figure 5. 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 75 125 165 Grass/Grasslike 1 20 70 Forb 1 10 30 Total 77 155 265 Table 6. Soil surface cover
Tree basal cover 0% Shrub/vine/liana basal cover 0-0% Grass/grasslike basal cover 0-0% Forb basal cover 0-0% Non-vascular plants 0% Biological crusts 10-30% Litter 10-30% Surface fragments >0.25" and <=3" 0-20% Surface fragments >3" 0-10% Bedrock 0% Water 0% Bare ground 30-90% Table 7. Canopy structure (% cover)
Height Above Ground (ft) Tree Shrub/Vine Grass/
GrasslikeForb <0.5 – 0-2% 0-5% 0-5% >0.5 <= 1 – 1-5% 0-5% 0-5% >1 <= 2 – 1-5% 1-10% 1-5% >2 <= 4.5 – 5-10% 0-2% 0-1% >4.5 <= 13 – – – – >13 <= 40 – – – – >40 <= 80 – – – – >80 <= 120 – – – – >120 – – – – State 2
Native shrubs and non native annualsCommunity 2.1
Native shrubs and non native annualsThis state occurs where perennial grasses have been eliminated by the interactions of fire, drought and continuous grazing. Native and non-native annual forbs and grasses dominate the herbaceous layer of the plant community.
Additional community tables
Table 8. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Dominant perennial grasses 1–35 tobosagrass PLMU3 Pleuraphis mutica 1–25 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 0–10 – bush muhly MUPO2 Muhlenbergia porteri 0–10 – alkali sacaton SPAI Sporobolus airoides 0–5 – big sacaton SPWR2 Sporobolus wrightii 0–5 – 2 Miscellaneous perennial grasses 0–10 purple threeawn ARPU9 Aristida purpurea 0–5 – blue threeawn ARPUN Aristida purpurea var. nealleyi 0–5 – spidergrass ARTE3 Aristida ternipes 0–5 – spidergrass ARTEG Aristida ternipes var. gentilis 0–5 – low woollygrass DAPU7 Dasyochloa pulchella 0–2 – whiplash pappusgrass PAVA2 Pappophorum vaginatum 0–2 – spike dropseed SPCO4 Sporobolus contractus 0–2 – sand dropseed SPCR Sporobolus cryptandrus 0–2 – mesa dropseed SPFL2 Sporobolus flexuosus 0–2 – false Rhodes grass TRCR9 Trichloris crinita 0–2 – poverty threeawn ARDI5 Aristida divaricata 0–2 – plains bristlegrass SEVU2 Setaria vulpiseta 0–1 – Arizona cottontop DICA8 Digitaria californica 0–1 – nineawn pappusgrass ENDE Enneapogon desvauxii 0–1 – 3 Annual grasses 0–25 needle grama BOAR Bouteloua aristidoides 0–10 – sixweeks grama BOBA2 Bouteloua barbata 0–10 – sixweeks fescue VUOC Vulpia octoflora 0–10 – sixweeks threeawn ARAD Aristida adscensionis 0–5 – prairie threeawn AROL Aristida oligantha 0–5 – mucronate sprangeltop LEPAB Leptochloa panicea ssp. brachiata 0–5 – Rothrock's grama BORO2 Bouteloua rothrockii 0–5 – Arizona brome BRAR4 Bromus arizonicus 0–2 – canyon cupgrass ERLE7 Eriochloa lemmonii 0–2 – desert lovegrass ERPEM Eragrostis pectinacea var. miserrima 0–2 – tufted lovegrass ERPEP2 Eragrostis pectinacea var. pectinacea 0–2 – delicate muhly MUFR Muhlenbergia fragilis 0–2 – littleseed muhly MUMI Muhlenbergia microsperma 0–2 – Bigelow's bluegrass POBI Poa bigelovii 0–2 – Arizona signalgrass URAR Urochloa arizonica 0–2 – Mexican sprangletop LEFUU Leptochloa fusca ssp. uninervia 0–1 – Forb4 Perennial forbs 1–5 dwarf desertpeony ACNA2 Acourtia nana 0–5 – weakleaf bur ragweed AMCO3 Ambrosia confertiflora 0–2 – hairyseed bahia BAAB Bahia absinthifolia 0–1 – desert marigold BAMU Baileya multiradiata 0–1 – stinging serpent CESI Cevallia sinuata 0–1 – whitemargin sandmat CHAL11 Chamaesyce albomarginata 0–1 – desert trumpet ERIN4 Eriogonum inflatum 0–1 – San Pedro daisy LAPO4 Lasianthaea podocephala 0–1 – lacy tansyaster MAPIP4 Machaeranthera pinnatifida ssp. pinnatifida var. pinnatifida 0–1 – desert tobacco NIOB Nicotiana obtusifolia 0–1 – Coues' cassia SECO10 Senna covesii 0–1 – silverleaf nightshade SOEL Solanum elaeagnifolium 0–1 – desert globemallow SPAM2 Sphaeralcea ambigua 0–1 – brownplume wirelettuce STPA4 Stephanomeria pauciflora 0–1 – pricklyleaf dogweed THAC Thymophylla acerosa 0–1 – rue of the mountains THTE2 Thamnosma texana 0–1 – brownfoot ACWR5 Acourtia wrightii 0–1 – trailing windmills ALIN Allionia incarnata 0–1 – 5 Annual forbs 0–25 flatcrown buckwheat ERDE6 Eriogonum deflexum 0–10 – cryptantha CRYPT Cryptantha 0–5 – wheelscale saltbush ATEL Atriplex elegans 0–5 – Coulter's spiderling BOCO2 Boerhavia coulteri 0–5 – carelessweed AMPA Amaranthus palmeri 0–5 – bristly fiddleneck AMTE3 Amsinckia tessellata 0–5 – desert Indianwheat PLOV Plantago ovata 0–5 – Gordon's bladderpod LEGO Lesquerella gordonii 0–5 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 0–5 – intermediate pepperweed LEVIM Lepidium virginicum var. medium 0–5 – coastal bird's-foot trefoil LOSAB Lotus salsuginosus var. brevivexillus 0–5 – slender goldenweed MAGR10 Machaeranthera gracilis 0–5 – Nuttall's povertyweed MONU Monolepis nuttalliana 0–5 – green carpetweed MOVE Mollugo verticillata 0–2 – tanseyleaf tansyaster MATA2 Machaeranthera tanacetifolia 0–2 – hairy desertsunflower GECA2 Geraea canescens 0–2 – star gilia GIST Gilia stellata 0–2 – Arizona poppy KAGR Kallstroemia grandiflora 0–2 – Coulter's lupine LUSP2 Lupinus sparsiflorus 0–2 – sorrel buckwheat ERPO4 Eriogonum polycladon 0–2 – Texas stork's bill ERTE13 Erodium texanum 0–2 – California poppy ESCAM Eschscholzia californica ssp. mexicana 0–2 – desert evening primrose OEPR Oenothera primiveris 0–2 – Florida pellitory PAFL3 Parietaria floridana 0–2 – combseed PECTO Pectocarya 0–2 – phacelia PHACE Phacelia 0–2 – woollyhead neststraw STMI2 Stylocline micropoides 0–2 – woolly tidestromia TILA2 Tidestromia lanuginosa 0–2 – white tackstem CAWR Calycoseris wrightii 0–2 – brittle spineflower CHBR Chorizanthe brevicornu 0–2 – hyssopleaf sandmat CHHY3 Chamaesyce hyssopifolia 0–2 – Esteve's pincushion CHST Chaenactis stevioides 0–2 – hairy prairie clover DAMO Dalea mollis 0–2 – American wild carrot DAPU3 Daucus pusillus 0–2 – western tansymustard DEPI Descurainia pinnata 0–2 – miniature woollystar ERDI2 Eriastrum diffusum 0–2 – fringed redmaids CACI2 Calandrinia ciliata 0–2 – exserted Indian paintbrush CAEXE Castilleja exserta ssp. exserta 0–1 – yellow tackstem CAPA7 Calycoseris parryi 0–1 – common woolly sunflower ERLA6 Eriophyllum lanatum 0–1 – hoary bowlesia BOIN3 Bowlesia incana 0–1 – milkvetch ASTRA Astragalus 0–1 – Arizona popcornflower PLAR Plagiobothrys arizonicus 0–1 – manybristle chinchweed PEPA2 Pectis papposa 0–1 – doubleclaw PRPA2 Proboscidea parviflora 0–1 – New Mexico plumeseed RANE Rafinesquia neomexicana 0–1 – sleepy silene SIAN2 Silene antirrhina 0–1 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 0–1 – Mexican fireplant EUHE4 Euphorbia heterophylla 0–1 – bristly nama NAHI Nama hispidum 0–1 – glandular threadplant NEGL Nemacladus glanduliferus 0–1 – Shrub/Vine6 Dominant shrubs 75–150 creosote bush LATR2 Larrea tridentata 25–75 – shadscale saltbush ATCO Atriplex confertifolia 1–25 – cattle saltbush ATPO Atriplex polycarpa 0–20 – mound saltbush ATOB Atriplex obovata 0–15 – fourwing saltbush ATCA2 Atriplex canescens 0–10 – whitethorn acacia ACCO2 Acacia constricta 0–5 – catclaw acacia ACGR Acacia greggii 0–1 – longleaf jointfir EPTR Ephedra trifurca 0–1 – American tarwort FLCE Flourensia cernua 0–1 – crown of thorns KOSP Koeberlinia spinosa 0–1 – water jacket LYAN Lycium andersonii 0–1 – pale desert-thorn LYPA Lycium pallidum 0–1 – mariola PAIN2 Parthenium incanum 0–1 – western honey mesquite PRGLT Prosopis glandulosa var. torreyana 0–1 – soaptree yucca YUEL Yucca elata 0–1 – lotebush ZIOB Ziziphus obtusifolia 0–1 – 7 Half shrubs 0–30 rayless goldenhead ACSP Acamptopappus sphaerocephalus 0–10 – burrobush AMDU2 Ambrosia dumosa 0–10 – littleleaf ratany KRER Krameria erecta 0–5 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–2 – rough menodora MESC Menodora scabra 0–2 – whitestem paperflower PSCO2 Psilostrophe cooperi 0–2 – desert zinnia ZIAC Zinnia acerosa 0–2 – threadleaf snakeweed GUMI Gutierrezia microcephala 0–1 – winterfat KRLA2 Krascheninnikovia lanata 0–1 – 8 Succulents 0–5 tulip pricklypear OPPH Opuntia phaeacantha 0–2 – buck-horn cholla CYAC8 Cylindropuntia acanthocarpa 0–1 – Christmas cactus CYLE8 Cylindropuntia leptocaulis 0–1 – walkingstick cactus CYSP8 Cylindropuntia spinosior 0–1 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 0–1 – candy barrelcactus FEWI Ferocactus wislizeni 0–1 – devil's cholla GRKU Grusonia kunzei 0–1 – cactus apple OPEN3 Opuntia engelmannii 0–1 – Table 9. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
This site offers little in the way for livestock grazing. Occasional use will be made of slopes less than 45% which have tobosa and shadscale.
Wildlife on the site is limited to small mammals and birds and their associated predators. Areas adjacent to major streams like the Gila River, may offer limited forage for mule deer.Hydrological functions
These soils are variable in texture from loams to clays, and can produce considerable amounts of runoff and sediment.
Recreational uses
Hunting, horseback riding, hiking, photography and bird-watching
Supporting information
Type locality
Location 1: Graham County, AZ Township/Range/Section T8S R28E S36 General legal description Gila River valley near Safford Contributors
Dan Robinett
Larry D. EllicottApproval
Curtis Talbot, 4/09/2021
Rangeland 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 08/19/2026 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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