Natural Resources
Conservation Service
Ecological site DX035X03B817
Loamy Slopes
17-25" p.z.
Cobbly (PIPO)
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
The soils on this ecological site are moderately deep to very deep. They are very flaggy to very cobbly throughout the soil profile. Surface textures range from very flaggy fine sandy loam to cobbly loamy sand. This ecological site occurs on steep knolls, footslopes, hills and backslopes of stable landslides and plateaus. Slopes average 15 to 60 percent, but can be steeper in spots.
Table 1. Dominant plant species
Tree (1) Pinus ponderosa
(2) Pseudotsuga menziesii var. glaucaShrub (1) Quercus gambelii
(2) Purshia tridentataHerbaceous (1) Poa fendleriana
(2) Carex geophilaLegacy ID
F035XH817AZ
Physiographic features
This ecological site occurs on steep knolls, footslopes, hills and backslopes of stable landslides and plateaus. Slopes average 15 to 60 percent, but can be steeper in spots. The soils are very flaggy to very cobbly throughout the soil profile. Surface textures range from loamy sands to fine sandy loams. Subsurface textures range from sandy loams to sandy clay loams.
Table 2. Representative physiographic features
Landforms (1) Knoll
(2) Ridge
(3) Hill
Flooding frequency None Ponding frequency None Elevation 7600 – 8500 ft Slope 15 – 60 % Aspect Aspect is not a significant factor 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
The soil moisture on this ecological site comes from precipitation. The site does not benefit significantly from run-on moisture. The sandy surface texture of the soil allows the site to capture the majority of both gentle winter storms and intense summer thunderstorms with little runoff.
Soil features
The soils on this ecological site are moderately deep to very deep. Surface textures range from very flaggy fine sandy loam to cobbly loamy sand. Subsoil textures range from gravelly sandy clay loam to very channery loamy sand. Parent material is aluvium and residuum from sandstone, basalt, and tuff-breccia.
Available water capacity is very low to moderate. Water erosion hazard is moderate to high; wind erosion is slight to high. Soils are non-saline and non-sodic. pH range is 6.1-8.4.
Soil survey map unit components that have been correlated to this ecological site include:
SSA-715 Ft. Defiance Area AZ/NM 068-Narbona family, 113-Sonsela;
SSA-717 Shiprock Area AZ/NM 600 & 614 Kunz,
606 & 608 Narbona, 610 & 612 Xankey, 71S onsela and 608 Zilditloi.Table 4. Representative soil features
Parent material (1) Alluvium – basalt
(2) Residuum – sandstone
Surface texture (1) Very flaggy fine sandy loam
(2) Very flaggy loam
(3) Very cobbly fine sandy loam
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Moderately slow to rapid Soil depth 40 – 80 in Surface fragment cover <=3" 0 – 35 % Surface fragment cover >3" 0 – 50 % Available water capacity
(0-40in)2 – 10 in Soil reaction (1:1 water)
(0-40in)6.1 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)0 – 35 % Subsurface fragment volume >3"
(Depth not specified)0 – 55 % 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.State and transition model
Custom diagramStandard diagram
Figure 4. 358 CobblySlopesPIPO 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 StateCommunity 1.1
Historic Climax Plant CommunityTree cover ranges 35-50% with the major overstory species being ponderosa pine and Douglas fir. Understory species include grasses, forbs, shrubs and small trees. In the herbaceous stage, grasses, shrubs and forbs dominate the site. Some small trees are present. In the immature stage young ponderosa pine are in balance with grasses, forbs and shrubby Gambel oak. In the mature/climax stage, ponderosa pine dominates the site. Gambel oak is abundant with grasses, some Douglas fir and shrubs.
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 165 275 385 Grass/Grasslike 90 150 210 Forb 30 50 70 Tree 15 25 35 Total 300 500 700 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). AZ3901 , 35.8 17-25" p.z. muttongrass. Growth begins in the 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 5 10 30 20 20 10 5 0 0 Community 1.2
Lighter OverstoryPatchy mature reduced canopy cover, with less cover in understory trees.
Dense and abundant shrub, grass, forb cover.Community 1.3
Short trees with dense overstoryPole sized trees with very dense overstory
Dense upper and lower canopies (50-60%) sparse understory.Pathway 1.1a
Community 1.1 to 1.2Partial removal of mature PIPO canopy achieved through timber harvest, or Bark beetle infestation. The reduced canopy results in higher production on the forest floor of grass, forbs and to some extent shrubs.
Conservation practices
Forest Land Management Pathway 1.2a
Community 1.1 to 1.3Removal of majority of mature PIPO canopy achieved through timber harvest, or Bark beetle infestation.
Conservation practices
Forest Land Management Pathway 1.2a
Community 1.2 to 1.3Openings are filled in by natural regeneration of Ponderosa pine, forming an even aged tight canopy of sapling to pole size PIPO
Pathway 1.3a
Community 1.3 to 1.1Trees mature and are thinned more heavily than 1.3b, through fire or timber harvest forming a patchy and mature canopy.
Conservation practices
Forest Stand Improvement Forest Land Management Pathway 1.3b
Community 1.3 to 1.2Trees mature and are thinned either naturally or through Pre-commercial thinning forming a mature canopy.
Conservation practices
Forest Stand Improvement Forest Land Management State 2
Grass and Forb DominatedCommunity 2.1
Grass and Forb DominatedSeverely (
Transition 1
State 1 to 2Catastrpohic removal of most trees to the point of no natural regeneration.
Restoration pathway 1
State 2 to 1Tree planting restores forest 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 (%) Grass/Grasslike1 Grasses 90–210 muttongrass POFE Poa fendleriana 10–75 – squirreltail ELELE Elymus elymoides ssp. elymoides 5–55 – White Mountain sedge CAGE Carex geophila 5–50 – blue grama BOGR2 Bouteloua gracilis 5–20 – nodding brome BRAN Bromus anomalus 5–10 – Grass, perennial 2GP Grass, perennial 5–10 – mountain muhly MUMO Muhlenbergia montana 5–10 – Forb2 Forbs 30–70 Forb, perennial 2FP Forb, perennial 3–15 – fleabane ERIGE2 Erigeron 3–15 – pingue rubberweed HYRI Hymenoxys richardsonii 3–15 – silvery lupine LUAR3 Lupinus argenteus 5–15 – ragwort SENEC Senecio 3–15 – Shrub/Vine3 Shrubs 155–345 Gambel oak QUGA Quercus gambelii 40–175 – creeping barberry MARE11 Mahonia repens 40–60 – antelope bitterbrush PUTR2 Purshia tridentata 40–60 – mountain snowberry SYOR2 Symphoricarpos oreophilus 30–50 – 4 Succulents 10–40 Navajo yucca YUBA2 Yucca baileyi 10–40 – Tree5 Trees 15–35 ponderosa pine PIPO Pinus ponderosa 5–10 – Rocky Mountain Douglas-fir PSMEG Pseudotsuga menziesii var. glauca 5–10 – Rocky Mountain juniper JUSC2 Juniperus scopulorum 3–9 – twoneedle pinyon PIED Pinus edulis 3–9 – 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 5-70 30-45 8-15 0 Rocky Mountain Douglas-fir PSMEG Pseudotsuga menziesii var. glauca Native 5-65 5-10 4-12 0 Table 8. Community 1.1 forest understory composition
Common name Symbol Scientific name Nativity Height (ft) Canopy cover (%) Grass/grass-like (Graminoids)muttongrass POFE Poa fendleriana Native – 10–20 Shrub/SubshrubGambel oak QUGA Quercus gambelii Native 1–20 30–40 Table 9. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 10. Community 1.3 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 11. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
Site has steep slopes and moderate production of forage. Cattle, sheep, goats and horses can graze in summer and fall. Slopes are steep and soils are rocky which hinder livestock movement and proper use. Young trees should not be grazed.
Water availability for wildlife comes from springs or man-made watering facilities. Cover is good for most species. A good variety of understory species makes forage good. Topography provides escape habitat.Recreational uses
Recreational activities include hiking, wildlife observations and hunting. Landscape quality is good.
Wood products
Site is suitable for crawler-tractor type equipment for site preparation and precommercial thinning. Tree planting should be done by hand. Equipment is limited by steep slopes. Unsurfaced roads are hindered by steep slopes, flaggs, cobbles and rock. Water erosion is moderate to high in cutover areas/bare ground and roads/trails/landings as steep slopes will accelerate erosion. Wind erosion is slight to high. Soil compaction potential is good because the soil and rock mix well. Rutting potential is low due to rocky material in the soil. Revegetation potential is low because of steep slopes and rocky soils.
Harvest trees on a sustained yield basis Steep slopes, rocky surfaces make harvesting difficult. Prescribed burning is not recommended. Mechanical tree removal is not recommended due to steep slopes and rocky soils. Control pests to prevent tree damage and loss. Fire hazard is low as the fuel load is usually low.
Replanting suitability is poor. Seedling mortality is moderate. Natural regeneration is slow, but will occur in time. Seedlings should not be grazed. Plant competition is moderate to severe. Windthrow hazard is sligh because of good rooting depth.Table 12. 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 65 70 300 335 70 – – ponderosa pine PIPO 65 70 325 335 – – – Rocky Mountain Douglas-fir PSMEG 60 66 240 250 – – – Rocky Mountain Douglas-fir PSMEG 60 66 225 250 65 – – Supporting information
Type locality
Location 1: San Juan County, NM Township/Range/Section T22N R19W S17 General legal description Toadlena Quad, Chuska Mountains, Navajo Reservation. 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
D. Schlicting, K. Gishi
HSH
Karlynn Huling
Larry D. Ellicott
Steve BarkerApproval
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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