Natural Resources
Conservation Service
Ecological site DX035X03B818
Sandy Loam Slopes
17-25" p.z.
Cobbly (PIPO, POTR5)
Last updated: 5/20/2025
Accessed: 04/30/2026
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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): 035X–Colorado Plateau
This ecological site occurs in Common Resource Area 35.8 - the Colorado Plateau Ponderosa Pine Forests
The Common Resource Area occurs within the Colorado Plateau Physiographic Province. Elevations range from 6800 to 8500 feet and precipitation averages 17 to 25 inches per year. Vegetation includes ponderosa pine, white fir, aspen, pinyon, juniper, Gambel oak, big sagebrush, ceanothus, blue elderberry, muttongrass, upland sedge, and big wildrye, mountain muhly, Arizona fescue, pine dropseed, and blue grama. The soil temperature regime ranges from mesic to frigid and the soil moisture regime is typic ustic. This unit occurs within the Colorado Plateau Physiographic Province and is characterized by a sequence of flat to gently dipping sedimentary rocks eroded into plateaus, valleys and deep canyons. Sedimentary rock classes dominate the plateau with volcanic fields occurring for the most part near its margin.Ecological site concept
Soils grouped on this site are moderately deep to very deep. Surface textures range from very gravelly sandy loam to very flaggy loamy sand. This ecological site is located on footslopes, sideslopes, backslopes of high plateaus, mesas, hills and structural benches. Slopes range from 15 to 60 percent.
Table 1. Dominant plant species
Tree (1) Pinus ponderosa
(2) Populus tremuloidesShrub (1) Symphoricarpos oreophilus
Herbaceous (1) Carex geophila
(2) Elymus elymoidesLegacy ID
F035XH818AZ
Physiographic features
This site is located on footslopes, sideslopes, backslopes of high plateaus, mesas, hills and structural benches.
Table 2. Representative physiographic features
Landforms (1) Hill
(2) Mountain slope
(3) Mountain valley
Flooding frequency None Ponding frequency None Elevation 7600 – 8500 ft Slope 15 – 60 % Aspect N, S Climatic features
Winter-Summer moisture ratios are typically 70:30 on the west side of this CRA and shift to 60:40 on the east side. Late spring is usually the driest period and early fall moisture can be sporadic. Summer rains fall from June through September; moisture originates in the Gulf of Mexico and creates convective, usually brief, intense thunderstorms. Cool season moisture from October through May tends to be frontal; it originates in the Pacific and the Gulf of California and falls in widespread storms with longer duration and lower intensity. Precipitation generally comes as snow from October into April. Snowpack can persist for 3-4 months, although it may disappear in exposed areas during prolonged dry weather. Summer daytime temperatures are typically 80-90 F but can exceed 95 F. Winter temperatures around 0 F are common and can reach -25 F.
Table 3 Representative climatic features
Frost-free period (average) 100 days Freeze-free period (average) 130 days Precipitation total (average) 30 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
This site occurs in an upland position. The soil moisture on this ecological site comes from precipitation. It does not benefit from run-in moisture but does sustain runoff.
Soil features
Soils on this site run are moderately deep to very deep. Surface textures range from very gravelly sandy loam to very flaggy loamy sand. Subsurface textures range from cobbly sandy clay loam to channery sandy loam. The soils are derived from alluvium, colluvium and residuum from sandstone. Hazard of erosion from water is moderate to high and from wind is high.
Soil survey map unit components that have been correlated to this ecological site include:
SSA-713 Chinle Area 1-Akhoni/Typic Argiustolls/Tuntsa, 58-Typic Haplustoll, moderately deep/Typic Ustipsamments;
SSA-715 Ft. Defiance Area AZ/NM 051-Klizhin family, 113-Washpass family/Viewpoint, 138 Zilditloi/Quamon family;
SSA 717 Shiprock Area AZ/NM MU's 710 & 704 Klizhin, 704 Captom and 708 Tunitcha.Table 4. Representative soil features
Parent material (1) Alluvium – sandstone
(2) Colluvium – basalt
(3) Residuum – tuff breccia
Surface texture (1) Fine sandy loam
(2) Very flaggy loamy sand
(3) Very gravelly loam
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Moderate to moderately rapid Soil depth 20 – 80 in Surface fragment cover <=3" 0 – 5 % Available water capacity
(0-40in)5 – 10 in Soil reaction (1:1 water)
(0-40in)6.1 – 7.3 Subsurface fragment volume <=3"
(Depth not specified)0 – 10 % Ecological dynamics
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 historic climax plant community for this ecological site has been described by sampling relict or relatively undisturbed sites and/or reviewing historic records. The historic climax plant community is the plant community that evolved over time with the soil forming process and long term changes in climatic conditions of the area. It is the plant community that was best adapted to the unique combination of environmental factors associated with the site.
Natural disturbances, such as drought, fire, grazing of native fauna, and insects, are inherent in the development and maintenance of these plant communities. The effects of these disturbances are part of the range of characteristics of the ecological site. Fluctuations in plant community structure and function caused by the effects of natural disturbances help establish the boundaries and characteristics of an ecological site. They are accounted for as part of the range of characteristics of the ecological site. Recognizable plant community phases are identified in the reference state of the ecological site. Some sites may have a small range of variation, while others have a large range. Some plant community phases may exist for long periods of time, while others may only occur for a couple of years after a disturbance.
Deterioration of the plant community, hydrology, or soil site stability on an ecological site can result in crossing a threshold or potentially irreversible boundary to another state, or equilibrium. This can occur as a result of the loss of soil surface through erosion, the loss of the stability of the site due to disturbances that cause active erosion on the site, increases in the amounts and/or patterns or runoff from rainstorms, changes in availability of surface and subsurface water, significant changes in plant structural and functional types, or the introduction of non-native species. When these thresholds are crossed, the potential of the ecological site to return to the historic climax plant community can be lost, or restoration will require significant inputs . There may be multiple states possible for an ecological site, determined by the type and or severity of disturbance.
The known states and transition pathways for this ecological site are described in the state and transition model. Within each state, there may be one or more known plant community phases. These community phases describe the different plant community that can be recognized and mapped across this ecological site. The state and transition model is intended to help land users recognize the current plant community on the ecological site, and the management options for improving the plant community to the desired plant community.
Plant production information in this site description is standardized to the annual production on an air-dry weight basis in near normal rainfall years.
T1 Catastrophic Wilfire or clear cut timber Harvest
R1 Tree PlantingState and transition model
Custom diagramStandard diagram
Figure 4. 358 SandyLoamSlopesCobbly S&T
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 2 submodel, plant communities
State 1
Reference Plant CommunutyThe reference plant community is dominated by tall trees including Ponderosa pine, Douglas fir and Quaking aspen. North facing slopes can be more mesic with Corkbark fir and Colorado blue spruce. The understory consists of grasses and grass-like plants such as Kentucky bluegrass and White Mountain sedge, forbs such as gerainium and senecio with shrubs such as mountain snowberry and Gambel oak and scattered tree reproduction.
Community 1.1
Historic Climax Plant CommunityMature ponderosa pine is dominant with quaking aspend and Douglas fir. Medium cover in small shrubs. Light to mid cover in Perennial bunch grasses. Light to mid cover in forbs.
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)Grass/Grasslike 80 160 240 Shrub/Vine 60 120 180 Forb 40 80 120 Tree 25 45 65 Total 205 405 605 Figure 6. Plant community growth curve (percent production by month). AZ3581 , 35.8 17-25" p.z. all sites. Growth begins in the spring, most growth occurs during the summer rainy season..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 0 4 10 24 21 23 13 5 0 0 Figure 7. Plant community growth curve (percent production by month). AZ3902 , 35.8 17-25" p.z. Arizona fescue. Growth begins in the late spring and extends through the summer rainy season..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 0 0 5 20 30 30 10 5 0 0 Community 1.2
Lighter OverstoryPatchy mature reduced canopy cover, with less cover in understory trees.
Dense and abundant grass and forb cover.Community 1.3
Short trees with dense overstoryPole sized trees with very dense overstory
Dense upper and lower canopies (50-60%) sparse understoryPathway 1.1
Community 1.1 to 1.2Partial removal of mature tree canopy through timber harvest, or Bark beetle infestation. The reduced canopy results in higher production on the forest floor of grass, forb and to some extent shrubs.
Conservation practices
Forest Land Management Pathway 1.2
Community 1.1 to 1.3The majority of mature trees are removed leaving only short immature trees.
Conservation practices
Forest Land Management Pathway 1.2
Community 1.2 to 1.3The majority of mature trees are removed leaving only short immature trees.
Conservation practices
Forest Land Management Pathway 1.3
Community 1.3 to 1.1Trees mature and are thinned either naturally or through Pre-commercial thinning forming a mature canopy.
Conservation practices
Forest Stand Improvement Forest Land Management Pathway 1.4
Community 1.3 to 1.2Trees mature and are thinned more heavily than 1.3, through fire or timber harvest forming a patchy and mature canopy.
Conservation practices
Forest Stand Improvement Forest Land Management State 2
Canopy removedCommunity 2.1
Canopy removedTrees removed to less that 5% overstory. Grasses, forbs and shrubs dominate.
Transition 1
State 1 to 2Catastrophic Wilfire or clear cut timber Harvest removes tree component from community.
Restoration pathway 1
State 2 to 1Tree planting restores tree component to community.
Conservation practices
Forest Land Management Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Tree0 Trees - understory (4.5') 20–60 Grass/Grasslike1 Grasses and Grasslikes 80–240 White Mountain sedge CAGE Carex geophila 10–60 – Kentucky bluegrass POPR Poa pratensis 20–40 – squirreltail ELELE Elymus elymoides ssp. elymoides 9–35 – Arizona fescue FEAR2 Festuca arizonica 9–20 – prairie Junegrass KOMA Koeleria macrantha 9–20 – muttongrass POFE Poa fendleriana 9–20 – Grass, perennial 2GP Grass, perennial 9–20 – nodding brome BRAN Bromus anomalus 9–20 – Ross' sedge CARO5 Carex rossii 9–20 – Forb2 Common Forbs 40–120 western yarrow ACMIO Achillea millefolium var. occidentalis 4–15 – nodding brome BRAN Bromus anomalus 0–15 – Arizona fescue FEAR2 Festuca arizonica 0–15 – prairie Junegrass KOMA Koeleria macrantha 0–15 – muttongrass POFE Poa fendleriana 0–15 – rosy pussytoes ANRO2 Antennaria rosea 4–15 – geranium GERAN Geranium 4–15 – pingue rubberweed HYRI Hymenoxys richardsonii 4–11 – silvery lupine LUAR3 Lupinus argenteus 4–11 – hairy brackenfern PTAQP2 Pteridium aquilinum var. pubescens 4–11 – ragwort SENEC Senecio 4–11 – Fendler's meadow-rue THFE Thalictrum fendleri 4–11 – pale agoseris AGGL Agoseris glauca 4–11 – Forb, perennial 2FP Forb, perennial 4–11 – Grass, perennial 2GP Grass, perennial 0–10 – Shrub/Vine3 Shrubs 60–180 mountain snowberry SYOR2 Symphoricarpos oreophilus 10–35 – Shrub (>.5m) 2SHRUB Shrub (>.5m) 8–25 – kinnikinnick ARUV Arctostaphylos uva-ursi 8–25 – common juniper JUCO6 Juniperus communis 8–25 – creeping barberry MARE11 Mahonia repens 8–25 – Gambel oak QUGA Quercus gambelii 8–25 – Woods' rose ROWO Rosa woodsii 8–25 – Table 7. Community 1.1 forest overstory composition
Common name Symbol Scientific name Nativity Height ft Canopy cover (%) Diameter in Basal area (square ft/acre) Treeponderosa pine PIPO Pinus ponderosa Native 10-85 45-55 8-15 0 quaking aspen POTR5 Populus tremuloides Native 15-70 10-15 5-10 0 Rocky Mountain Douglas-fir PSMEG Pseudotsuga menziesii var. glauca Native 5-70 5-10 4-10 0 Table 8. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 9. Community 1.3 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 10. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
Suitability for grazing by livestock is good before canopy exceeds 50%. Cattle, sheep, goats and horses can use this site in summer and early fall. Management considerations include use of Prescribed Grazing, water developments and reseeding grass following harvest operations for forage and to reduce erosion, grazing should not damage young trees.
Site factors affecting wildlife:
Water: Frequently found in scattered natural wetlands and springs.
Cover: good for most species.
Food: Good potential except where grazing is unmanaged.
Other: Snowfall causes shifts in wildlife populations.
Recreational uses
Landscape quality is good and recreational activities include hiking, camping, horseback riding, wildlife observations and photography
Wood products
Gambel oak and Ponderosa pine provide opportunities for firewood collection when dead and down.
Other information
Woodland Overstory Production:
PIPO PSMEG POTRT
Site Index: 83 72 73
Fuelwood (Cords/Ac):
Fence posts (7ft)/Ac:
Christmas Trees/Ac:
CMAI* per year:(bd ft/ac)440 290 255
Productivity Class: 5 3 3
* CMAI is the "Culmination of Mean Annual Increment" or highest average growth rate of the stand in the units specified.
Woodland Uses and Interpretations
Equipment Suitability:
Harvesting: On Slopes greater than 20% use crawler-type equipment
Site Preparation: Same
Tree Planting: Best done by hand
Precommercial thinning: use crawler-type equipment
Equipment Limitations:
Slope: Moderate-Severe for all equipment
Unsurfaced roads: Slope most limiting factor
Stoniness/Rock Outcrop: Some stones and rock outcrop present
Water Table/Flooding: None
Erosion potentials:
Cutover areas/bare ground: Water - moderate-high
Wind - slight-high
Roads/Trails/Landings: Water - moderate-high soil compaction
Wind - slight-high
Soil Management:
Compaction potential: Good - soil workable, has good shear strength
Rutting potential: Some rutting may occur when wet
Revegetation potential: Good - slope most limiting
Silviculture potentials & limitations:
Harvest Cutting: harvest select mature trees on slopes less than 30%. Final removal cuts and intermediate cuts are desirable.
Thinning & Improvement: Thick stands need thinned to improve growth rates of trees left.
Prescribed burning: Periodic ground fires will reduce any understory build up. Slope may limit any fire control
Mechanical Tree Removal: Slope would prohibit use of heavy equipment.
Pest Control: Control pests to prevent tree damage & loss
Fire Hazard: Fire hazard may become extreme if understory fuel load builds up.
Suitability for replanting: Fair - slope is prohibitive.
Seedling Mortality: Slight-moderate slope exposure may be prohibitive.
Natural Regeneration: Slight limitations.
Seedling Protection: Seedlings should be protected from grazing and trampling
Plant competition: Dense grass and forb cover may impede regeneration.
Windthrow Hazard: Slight-moderate rooting depth is generally greater than 30 inches.
Table 11. Representative site productivity
Common name Symbol Site index low Site index high CMAI low CMAI high Age of CMAI Site index curve code Site index curve basis Citation ponderosa pine PIPO 80 85 420 440 83 – – ponderosa pine PIPO 75 83 430 440 – – – Rocky Mountain Douglas-fir PSMEG 70 74 275 290 72 – – Rocky Mountain Douglas-fir PSMEG 70 72 285 290 – – – quaking aspen POTR5 70 75 240 255 73 – – quaking aspen POTR5 70 73 250 255 – – – Supporting information
Type locality
Location 1: San Juan County, NM Township/Range/Section T22N R20W S11 General legal description Toadlena Quad on Chuska Mountains - Navajo Reservation - New Mexico. Other references
Updates and revisions for this ESD were conducted as part of a 2007-2012 Interagency Technical Assistance Agreement between the Bureau of Indian Affairs–Navajo Region and the NRCS-Arizona.
Contributors
Dan Carroll
Harmon S. Hodgkinson
Karlynn Huling
Larry D. EllicottApproval
Kendra Moseley, 5/20/2025
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 04/30/2026 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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