Subsection M261Ei
Sierra Valley

Lithology and Stratigraphy.   Quaternary lacustrine deposits dominate this subsection.  There are small areas of Quaternary alluvial deposits around the margins of Sierra Valley and in tributary valleys.

Geomorphology.   Most of the subsection is on nearly level basin floor that was occupied by a shallow Pleistocene lake.  There are sloping to nearly level alluvial fans and floodplains around the margins of the basin and in tributary valleys.  The elevation ranges from about 4900 feet on the basin floor up to about 5400 feet on alluvial fans.  Faulting and fluvial erosion and deposition are the main geomorphic processes.

Soils.  The soils are mostly Pachic and Aquic Argixerolls, Aridic Haploxerolls, Typic Haplaquolls, and Aquic Natrargids, plus Abruptic Xerollic Durargids on alluvial fans on the east side of the valley.  The soils are well to poorly drained.  Soil temperature regimes are mesic.  Soil moisture regimes are xeric on the west side, commonly aquic on the basin floor, and aridic on the east side of the valley.

Vegetation.   The predominant natural plant communities are Big sagebrush series and Sedge meadow communities.  Jeffrey pine series occurs on the south and west margins of Sierra Valley.

Characteristic series by lifeform include:
Grasslands: Ashy ryegrass series, Breaked sedge series, Idaho fescue series, Montane meadow habitat, Needle-and-thread series, Rocky Mountain sedge series.
Shrublands: Big sagebrush series, Bitterbrush series, Low sagebrush series, Parry rabbitbrush series, Rubber rabbitbrush series.
Forests and woodlands: Aspen series, Jeffrey pine series.

Surface Water.  Runoff is slow from most of the area.  The runoff flows through the Middle Fork of the Feather River.