Ecological Sections: Sierra Nevada - (MAP)
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.
Glaciated Batholith and Volcanic Flows
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.
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.
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:
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.
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
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.
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.