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Ecological Sections: Sierra Nevada - (MAP)

Subsection M261Ef
Granitic and Metamorphic Hills

This 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.

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.

Geomorphology.   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 soils.

    Characteristic series by lifeform include:
    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.
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.

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. 

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