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Ecological Sections: Sierra Nevada - (MAP)

Subsection M261Ek
Glaciated Batholith and Volcanic Flows

This subsection is along the crest of the Sierra Nevada from the Crystal Range southwest of Lake Tahoe to Kennedy Peak just south of Sonora Pass.   It has a cold to very cold and humid climate.  MLRA 22e.

Lithology and Stratigraphy.   Mesozoic granitic and post-batholith volcanic rocks predominate in this subsection; pre-batholith rocks are sparse.  Mesozoic mafic plutonic rocks are common.  The volcanic rocks are mostly Pliocene andesite and lahars of the Mehrten Formation.  The pre-batholith rocks are mostly metamorphosed Jurassic marine sedimentary and early Mesozoic volcanic rocks.  Pleistocene glacial till and outwash are common and there are small areas of Quaternary alluvial and lacustrine deposits.

Geomorphology.   This subsection is characterized by steep mountains that rise above the plateau west of the crest and have deep V- to U-shaped canyons.  Glacial erosion has modified most of the landforms.  Cirques, aretes, cols, horns, and smooth, striated bedrock are common.  The moraines have been modified by fluvial erosion.  Some of the rivers flow in the bottoms of very steep sided canyons.  The elevation ranges from about 7000 up to 11,570 feet on Leavitt Peak.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Dystric Xeropsamments; Entic, Typic, and Pachic Xerumbrepts; and Cryumbrepts.  Much of the granitic rock is barren, lacking soil.  There are Andic and Lithic Cryumbrepts on volcanic rocks.  The soils are mostly well drained.  Soil temperature regimes are mostly frigid and cryic.  Soil moisture regimes are mostly xeric.  Soils have udic moisture regimes where snow persists through spring, melting to keep soils moist through much of the summer.   Soils with aquic moisture regimes are present in glaciated terrain and small valleys,  but they are not extensive.

Vegetation.   Most of this subsection is sparsely vegetated.  The main natural plant communities are Mixed subalpine forest series and Red fir series and communities of Subalpine meadow habitats.  Jeffrey pine series is common on shallow and rocky soils.  There are a few small patches of Mountain hemlock series at high elevations, and Aspen series occurs at lower elevations.  Lodgepole pine series prevails on many wet soils and on drier soils where cold air drainage and frost limit the regeneration of other conifers.  Aspen series is common where drifted snow accumulates and provides water during summer.  Sedge meadow communities are common, but they are not extensive.

    Characteristic series by lifeform include:
    Grasslands: Alpine habitat, Breaked sedge series, Fen habitat, Green fescue series, Montane meadow habitat, Mountain heather - bilberry series, Nebraska sedge series, Rocky Mountain sedge series, Rothrock sagebrush series, Shorthair reedgrass series, Shorthair sedge series, Subalpine meadow habitat.
    Shrublands: Bush chinquapin series, Greenleaf manzanita series, Huckleberry oak series, Mountain whitethorn series, Subalpine upland shrub habitat, Subalpine wetland shrub habitat, Tobacco brush series.
    Forests and woodlands: Aspen series, Lodgepole pine series, Mixed subalpine forest series, Mountain hemlock series, Red fir series, Western white pine series, Whitebark pine series.
Climate.  The mean annual precipitation is about 40 to 60 inches; most of it falls as snow.  Mean annual temperature is about 30 to 40 F.  The mean freeze-free period ranges from less than 25 to about 50 days.

Surface Water.  Runoff is rapid from most of the area.  Most of the runoff flows to the American, Cosumnes, Mukelumne, or Stanislaus Rivers on the west or to Lake Tahoe or the Carson or Walker Rivers on the east.  Maximum flow in these rivers is during spring when snow is melting rapidly.  There are many small natural lakes or ponds in glaciated terrain, and some reservoirs. 



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