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Ecological Sections: Sierra Nevada - (MAP)

Subsection M261Ec

This subsection is in mostly Tertiary volcanic terrain north of Sierra Valley.  It has a temperate to cold, semi-arid to subhumid climate.  MLRAs 21e and 22e.

Lithology and Stratigraphy.   Miocene andesite and pyroclastic rocks predominate in this subsection.  There are lesser amounts of Pliocene basalt and pyroclastic rocks, some exposures of Mesozoic granitic rocks, and, on the western edge of the subsection, early Tertiary and Paleozoic sedimentary rocks.  Quaternary alluvial and lacustrine deposits have accumulated in valleys.

Geomorphology.   Steep mountain and moderately steep hill slopes predominate in this subsection.  Alluvial fans, floodplains, terraces, and basin floors are present but much less extensive.  Most of the faults, and mountains that are elongated, are aligned toward the northwest.  The elevation ranges from about 5000 feet adjacent to Sierra Valley up to 8323 feet on Dixie Mountain and 8372 feet on Mt. Ingalls.  Faulting, mass wasting, and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Ultic Argixerolls, Ultic Haploxeralfs, Andic Xerumbrepts, and a diverse group of shallow soils, plus Dystric Xeropsamments, Entic Haploxerolls, and Entic and Dystric Xerochrepts on granitic rocks.  There are Cumulic Endoaquolls, Aridic Haploxerolls, and Aridic and Pachic Argixerolls on alluvial and lacustrine  deposits. The soils are mostly well drained and some are poorly drained.  Soil temperature regimes are mostly frigid, with some mesic in valleys.  Soil moisture regimes are mostly xeric, but some are aridic and some in valleys are aquic.

Vegetation.   The predominant natural plant communities are Jeffrey pine series, Mixed conifer series, and White fir series.  There are small areas of Red fir series at the highest elevations, plus Mountain hemlock series on Mt. Ingalls.  Western juniper series occurs on some shallow soils.  Big sagebrush is common in valleys.  The most common streamside riparian communities are Black cottonwood at lower elevations and Mountain alder series at higher elevations.  Aspen series occurs in some moist habitats.  Sedge meadow communities occur in wet areas.

    Characteristic series by lifeform include:
    Grasslands: Alpine habitat, Ashy ryegrass series, Breaked sedge series, Green fescue series, Idaho fescue series, Montane meadow habitat, Nebraska sedge series, Needle-and-thread series, Rocky Mountain sedge series.
    Shrublands: Big sagebrush series, Bitterbush series, Bush chinquapin series, Deerbrush series, Greenleaf manzanita series, Huckleberry oak series, , Mountain whitethorn series, Tobacco brush series, Wedgeleaf ceanothus series.
    Forests and woodlands: Aspen series, Incense-cedar series, Jeffrey pine series, Jeffrey pine - Ponderosa pine series, Mixed conifer series, Mountain hemlock series, Mountain juniper series, Ponderosa pine series, Red fir series, Western white pine series, White fir series, Whitebark pine series.
Climate.  The mean annual precipitation is about 15 to 30 inches; much of it falls as snow.  Mean annual temperature is about 40 to 50 F.  The mean freeze-free period is about 50 to 100 days.

Surface Water.  Runoff is rapid from most of the area, but slow on the basin floors.  The runoff flows to tributaries of the Feather River.  There are large reservoirs, Lake Davis and Frenchman Lake, in two valleys.

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