subsection is the low to intermediate elevations of the western slope of
the Sierra Nevada where it is crossed by the Feather and Yuba Rivers.
It has a temperate and humid climate. MLRA 22c.
Granitic and Metamorphic Hills
Lithology and Stratigraphy. Mesozoic granitic rocks
and Jurassic - Triassic metavolcanic rocks are most extensive in this subsection.
Paleozoic marine sedimentary, ultramafic, and mafic plutonic rocks are
moderately extensive. There are small areas of basalt and andesite
in the northern part of the subsection, and andesitic lahar along the southeastern
edge of the subsection. Quaternary alluvium and glacial till are
present, but not extensive.
This subsection is on a gently sloping to moderately steep plateau that
is crossed by the North, Middle, and South Forks of the Feather River and
the North Yuba, Middle Yuba, and South Yuba Rivers. These rivers
run in the bottom of very steep sided canyons that are as much as 2000
feet below the plateau surface. The elevation ranges from about 1000
feet up to 6095 feet on Table Mountain, but most of the rolling plateau
is below 5000 feet in this subsection. Fluvial erosion and, in the
river canyons, mass wasting are the main geomorphic processes.
Soils. The soils are mostly Typic, Dystric, and shallow
Dystric Xerochrepts; Mollic and Ultic Haploxeralfs; Lithic Xeropsamments;
and shallow Entic Haploxerolls on granitic rocks; plus Typic Haploxerults;
Xeric Haplohumults; Lithic and Dystric Lithic Xerochrepts; and Ultic Palexeralfs
on other kinds of rocks. The soils are well drained. Soil temperature
regimes are mostly mesic. Soil moisture regimes are xeric.
Vegetation. The predominant natural plant community
is Mixed conifer series. Douglas-fir - tanoak series is common in
areas of greater precipitation. There is some Ponderosa pine series at
lower elevations, Canyon live oak series on very steep, rocky canyon sideslopes,
and Mixed chaparral shrublands on steep south-facing slopes with shallow
Characteristic series by lifeform include:
Climate. The mean annual precipitation is about 40 to 80 inches;
much of it falls as snow. Mean annual temperature is about 45°
to 60° F. The mean freeze-free period is about 100 to 200 days.
Grasslands: Ashy ryegrass series, California oatgrass series,
Idaho fescue series, Montane meadow habitat, Needle-and-thread series.
Shrublands: Brewer oak series, Chamise series, Deerbrush series,
Greenleaf manzanita series, Interior live oak series, Tobacco brush series,
Wedgeleaf ceanothus series.
Forests and woodlands: Birchleaf mountain-mahogany series, Black
oak series, Canyon live oak series, Douglas-fir series, Douglas-fir - Ponderosa
pine series, Douglas-fir - tanoak series, Incense-cedar series, Mixed conifer
series, Ponderosa pine series, Tanoak series.
Surface Water. Runoff is rapid from most of the area.
Most of the runoff flows to the Feather River or Yuba River or tributaries
of them. There are no natural lakes, but some reservoirs.