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.

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): 028A–Ancient Lake Bonneville

MLRA 28A occurs in Utah (82 percent), Nevada (16 percent), and Idaho (2 percent). It encompasses approximately 36,775 square miles (95,246 square kilometers). A large area west and southwest of Great Salt Lake is a salty playa. This area is the farthest eastern extent of the Great Basin Section of the Basin and Range Province of the Intermontane Plateaus. It is an area of nearly level basins between widely separated mountain ranges trending north to south. The basins are bordered by long, gently sloping alluvial fans. The mountains are uplifted fault blocks with steep side slopes. Most of the valleys are closed basins containing sinks or playa lakes. Elevation ranges from 3,950 to 6,560 feet (1,204 to 2000 meters) in the basins and from 6,560 to 11,150 feet (1996 to 3398 meters) in the mountains. Much of the MLRA has alluvial valley fill and playa lakebed deposits at the surface from pluvial Lake Bonneville, which dominated this MLRA 13,000 years ago. A level line of remnant lake terraces on some mountain slopes indicates the former extent of this glacial lake. The Great Salt Lake is what remains of the pluvial lake.

Mountains in the interior of this MLRA consist of tilted blocks of marine sediments from Cambrian to Mississippian age with scattered outcrops of Tertiary continental sediments and volcanic rocks. The average annual precipitation is 5 to 12 inches (13 to 30 cm) in the valleys and ranges up to 49 inches (124 cm) in the mountains. Most of the rainfall in the southern LRU occurs as high-intensity, convective thunderstorms during the growing season (April through September). The driest period is from midsummer to early autumn in the northern LRU. Precipitation in winter typically occurs as snow. The average annual temperature is 39 to 53 °F (4 to 12 °C). The freeze-free period averages 165 days and ranges from 110 to 215 days, decreasing in length with increasing elevation. The dominant soil orders in this MLRA are Aridisols, Entisols, and Mollisols. Soils are dominantly in the mesic or frigid soil temperature regime, aridic or xeric soil moisture regime, and mixed mineralogy. The soils are generally well drained, loamy or loamy-skeletal, and very deep.

LRU notes

The Salt Desert/Wetland LRU consists of all the run-in ecological sites. Run-in sites occur in landform positions that receive additional moisture either through overland flow or subsurface water flow. Typical landforms are basin floors, lake plains, low lake terraces, depressional areas, drainageways, and flood plains. Sites within this LRU typically have water table depths of less than 60 inches (152 cm). Wetland plants, pickleweed (Salicornia sp.) and/or greasewood (Sarcorbatus vermiculatus) are dominant in the plant communities.

Ecological site concept

The Semiwet Fresh Streambank site occurs on flood plains and floodplain steps on slopes less than 4 percent. It can be found at elevations between 4,500 to 5,900 feet. The water table is typically between 18 and 72 inches below the soil surface. The Semiwet Fresh Streambank site is not directly adjacent to to the stream, but on the fluvial surface further out from the channel. The Semiwet Fresh Streambank will have a deeper water table than the Wet Fresh Streambank site and will not be flooded regularly. Flooding occurs occasionally to rarely and briefly to very briefly. The dominant plants are Fremont cottonwood (Populus fremontii), coyote willow (Salix exigua), and a herbaceous understory. The plant community will typically only develop under a certain set of circumstances. Cottonwoods need bare, moist soil to establish. The plant community has to be positioned far enough away from the stream channel to not experience frequent flooding but close enough to have a water table within 60 inches of the soil surface during the growing season.

Associated sites

Similar sites

Table 1. Dominant plant species