Ecological site group description

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.

Physiography

This group of ecological sites occur on structural benches, ledges, cuestas, plateaus, and mesas. Some sites receive extra moisture in the form of run off from adjacent rock outcrop. Other sites are associated with bedrock ledges on escarpments. Runoff ranges from low to very high. Slopes range from 2 to 80 percent and elevations range from 3900 to 6900 feet.

Climate

The climate is characterized by hot summers, cool winters. Climate is often modified by local topographic conditions. For example, cliff faces can appreciably modify both precipitation and temperature patterns. March, April and July through October are the wettest months of the year with May, June and November through February being the driest. Approximately 65 to 70% of the precipitation occurs as rain from May through October. Much of the summer precipitation occurs as convection thunderstorms. Precipitation is extremely variable from month to month and from year to year but averages between 6-16 inches. Large fluctuations in daily temperatures are common. Windy conditions are common year round, but the winds are strongest and most frequent during the spring.

Soil features

Soils in this group of ecological sites are typically very shallow or shallow and range in texture from sand to silty clay loam. Parent material includes colluvium, eolian deposits, slope alluvium and residuum from sandstone and interbedded sandstone, siltstone, and shale. Soils formed in eolian deposits on dipslopes, wide benches and mesa tops are sandy and often receive run-in moisture from surrounding expanses of sandstone. Soils formed in colluvium and residuum on scarp slopes of cuestas and escarpments on the sides of benches, mesas and plateaus tend to be so steep that much precipitation or run-in from the adjacent outcrops runs off downslope. Soil temperature regime is mesic and soil moisture regime is aridic or aridic ustic.

Vegetation dynamics

The ecological sites in this group are characterized by a sparse canopy of shrubs at lower elevation and Utah juniper and two-needle pinyon with a shrub understory at higher elevations. The herbaceous understory is sparse and typically dominated by perennial grasses in the reference states. Forbs are often linked to precipitation events and seed sources. In degraded states invasive annuals often become established. Much of the surface in these sites is made up of rock; either in the form of outcrops, slickrock or rock fragment cover ranging in size from gravel to boulders.
Major influences on these sites appear to be climatic variations and insect damage. These are not preferred sites for grazing due to sparse forage, steep slopes, stones, and broken topography. Invasive annuals, such as cheatgrass, can exploit any unused resources that may be present in a given year.

Major Land Resource Area

MLRA 035X
Colorado Plateau

Subclasses

• R035XB255AZ–Sandstone Rockland 6-10" p.z.
• R035XY019UT–Shallow Sand Rock Pocket (Utah Juniper/Two-Needle Pinyon)
• R035XY146UT–Desert Very Steep Stony Loam (Shadscale)
• R035XY240UT–Semidesert Steep Shallow Loam (Utah Juniper-Two-Needle Pinyon)
• R035XY325UT–Upland Very Steep Shallow Loam (Pinyon-Utah Juniper)

Correlated Map Unit Components

22966935, 22966803, 22967001, 22967000, 22966999, 22966895, 22966739, 22966940, 22966819, 22966806, 22966783, 22966782, 22966845, 22966934, 22966864, 22967010, 22966814, 22966853, 22966807

Stage

Provisional

Contributors

Vic Parslow
Keith Crossland
Curtis Talbot