subsection comprises Sierra Valley, which is in the block-faulted part
of the Sierra Nevada, at the head of the Middle Fork of the Feather River.
It has a temperate, semi-arid to subhumid climate. MLRA 21e.
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
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.
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:
Climate. The mean annual precipitation is about 10 to 25 inches;
most of it falls as snow. Mean annual temperature is about 45°
to 48° F. The mean freeze-free period is about 50 to 100 days.
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.