Natural Resources
Conservation Service

Ecological site F038XA132AZ

Basalt Hills
12-16
(JUOS, PIED)

Last updated: 9/05/2019
Accessed: 09/21/2026

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General information

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): 038X–Mogollon Transition South

AZ 38.1 – Lower Mogollon Transition

Elevations range from 3,000 to 4,500 feet and precipitation averages 12 to 16 inches per year. Vegetation includes canotia, one-seed juniper, mesquite, catclaw acacia, jojoba, turbinella oak, ratany, shrubby buckwheat, algerita, skunkbush, tobosa, vine mesquite, bottlebrush squirreltail, grama species, curly mesquite, desert needlegrass, and New Mexico feathergrass. The soil temperature regime is thermic and the soil moisture regime is ustic aridic. This MLRA occurs within the Transition Zone Physiographic Province and is characterized by canyons and structural troughs or valleys. Igneous, metamorphic, and sedimentary rock classes occur on rough mountainous terrain in association with less extensive sediment filled valleys exhibiting little integrated drainage.

Ecological site concept

The Basalt Hills ecological site occurs on hills. The soils on this site are shallow and well drained. They are formed in alluvium from basalt and pyroclastics.

Table 1. Dominant plant species

Tree	(1) Juniperus osteosperma (2) Pinus edulis
Shrub	(1) Ceanothus greggii (2) Purshia stansburiana
Herbaceous	(1) Poa fendleriana

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Physiographic features

The Basalt Hills ecological site occurs on hills.

Table 2. Representative physiographic features

Landforms	(1) Hill
Elevation	3000 – 4500 ft
Slope	15 – 65 %
Aspect	Aspect is not a significant factor

Climatic features

Precipitation in this common resource area averages 12 to 16 inches annually. The winter/summer rainfall ratio ranges from about 60/40 percent in the northwest part of the area to 50/50 percent in the southeast part. Summer rains fall July through September; are from high-intensity, convective thunderstorms. This moisture originates primarily from the Gulf of Mexico, but can come from the remnants of Pacific hurricanes in September. Winter moisture is frontal, originates in the north Pacific, and falls as rain or snow in widespread storms of low intensity and long duration. Snowfall ranges from a trace to 10 inches per year and can occur from November through March. Snow seldom persists for more than a day except on north aspects. May and June are the driest months of the year. Humidity is generally low all year. Average annual air temperatures range from 59 to 70 degrees F (thermic temperature regime). Daytime temperatures in the summer are commonly in the high 90’s. Freezing temperatures are common from October through April, usually during the night or early morning hours. The actual precipitation, available moisture, and temperature vary, depending on region, elevation, rain shadow effect, and aspect.

Table 3 Representative climatic features

Frost-free period (average)	230 days
Freeze-free period (average)	290 days
Precipitation total (average)	20 in

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Figure 2. Monthly precipitation range

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Figure 3. Monthly average minimum and maximum temperature

Soil features

The soils on the Basalt Hills ecological site are shallow and well drained. They are formed in alluvium from basalt and pyroclastics. The surface textures range from cobbly clay loam to extremely cobbly clay loam. The subsurface textures range from cobbly clay to extremely cobbly clay loam.
Soils mapped on this site includes: SSA-697 Mohave County Central Part MU, Thimble-142.

Table 4. Representative soil features

Parent material	(1) Alluvium – basalt
Surface texture	(1) Very cobbly clay loam
Family particle size	(1) Clayey
Drainage class	Well drained to somewhat excessively drained
Permeability class	Moderately slow to slow
Soil depth	10 – 20 in
Surface fragment cover <=3"	10 – 30 %
Surface fragment cover >3"	25 – 40 %
Available water capacity (0-40in)	0 – 2.5 in
Calcium carbonate equivalent (0-40in)	1 – 10 %
Subsurface fragment volume <=3" (Depth not specified)	0 – 10 %
Subsurface fragment volume >3" (Depth not specified)	10 – 20 %

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 grazing, fire, 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 shown for the group. Divide the resulting total by the total normal year production shown in the plant community description. If 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

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

State 1
Herbaceous-Woody: less than 50% Tree Canopy

Reference State that is mostly herbaceous with less than 50% tree canopy

Community 1.1
Mature Successional Stage

Mature Successional Stage: summer shortgrass, coniferous tree, summer perennial forb, summer midgrass, evergreen tree, summer annual forb, spring midgrass

Community 1.2
Immature Successional Stage

Immature Successional Stage: summer shortgrass, summer midgrass, spring midgrass, summer perennial forb, evergreen tree, coniferous tree, spring perennial forb

Community 1.3
Young Successional Stage

Young Successional Stage: summer peennial forb, evergreen tree, summer shortgrass, spring annual forb, summer perennial grasslike, spring perennial forb, summer midgrass

Pathway P 1.1A
Community 1.1 to 1.3

Stand replacing crown fire, drought with bark beetle infestations, mechanical brush control or forest stand improvement.

Pathway P 1.2A
Community 1.2 to 1.1

80-100 years of growth without a fire hot enough to kill young trees

Pathway P 1.2B
Community 1.2 to 1.3

Stand replacing crown fire

Pathway P 1.3A
Community 1.3 to 1.2

15-20 years of growth without a fire hot enough to kill young trees

State 2
Woody-Herbaceous: greater than 50% tree canopy

Woody-herbaceous with greater than 50% tree canopy

Community 2.1
Mature Successional Stage

Evergreen tree, spring perennial forb, evergreen shrub, summer midgrass, fern summer perennial forb, summer tallgrass

Transition T1A
State 1 to 2

Lack of fire, continuous heavy grazing

Restoration pathway R1A
State 2 to 1

Forest Stand Improvement or Brush Managment (mechanical), Prescribed Grazing

Additional community tables

Table 5. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 6. Community 1.2 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 7. Community 1.3 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 8. Community 2.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Supporting information

Type locality

Location 1: Mohave County, AZ
Township/Range/Section	T21N R11W S22
General legal description	Type location of Thimble series is about 930 feet south and 30 feet east of the northwest corner of sec. 22, T. 21 N., R. 11 W.

Contributors

Karlynn Huling
Larry D. Ellicott

Approval

Scott Woodall, 9/05/2019

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
Approved by
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
Presence of water flow patterns:
Number and height of erosional pedestals or terracettes:
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Number of gullies and erosion associated with gullies:
Extent of wind scoured, blowouts and/or depositional areas:
Amount of litter movement (describe size and distance expected to travel):
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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:
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Average percent litter cover (%) and depth ( in):
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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:
Perennial plant reproductive capability:

Download reference sheet

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