Mojave River Valley Museum
Ecological Sections: Sierra Nevada - (MAP)
subsection extends from the northwestern edge of the Sierra Nevada, adjacent
to Lake Almanor, along the Plumas Trough to Mohawk Valley. It has
a temperate to cold, subhumid to humid climate. MLRAs 22d and 22e.
Greenville - Graeagle
Lithology and Stratigraphy. Strongly folded basement
rocks predominate in this subsection. They include Triassic marine sedimentary
and Paleozoic marine sedimentary and metavolcanic rocks. There is
a large intrusion of Mesozoic ultramafic rock in the Red Hill area.
Quaternary alluvial and lacustrine deposits are moderately extensive in
Indian, Genessee, Meadow, American, and Mohawk Valleys.
Steep mountain and moderately steep hill slopes in the Plumas trough and
on both sides of it predominate in this subsection. Alluvial fans,
floodplains, terraces, and basin floors are moderately extensive.
The Plumas trough is an active northwest trending tectonic zone that separates
the main part of the Sierra Nevada on the southwest from the block faulted
part of the Sierra Nevada on the northeast. The elevation ranges
from about 2500 feet along the Feather River up to 6341 feet on Red Hill
and 6362 feet on Rush Creek Hill. Faulting, mass wasting, and fluvial
erosion and deposition are the main geomorphic processes.
The soils are mostly Ultic Haploxeralfs, Dystric Lithic Xerochrepts, Ultic
Palexeralfs, and Typic Haploxerults. They are mostly Lithic Haploxerolls,
Typic Xerochrepts, and Ultic Haploxeralfs on ultramafic rocks. There
are Cumulic Endoaquolls and Typic and Cumulic Haplaquolls on basin floors.
The soils are mostly well drained, but mostly poorly drained on basin floors.
Soil temperature regimes are mostly mesic. Soil moisture regimes
are mostly xeric, but aquic on basin floors.
The predominant natural plant community
is Mixed conifer series with Ponderosa pine series on south-facing slopes
and Jeffrey pine series on ultramafic rocks. Jeffrey pine series
is also common in the drier southeast part of the subsection. There
is some White fir series at higher elevations. Canyon live oak series
occurs on steep rocky slopes. The most common streamside riparian
communities are Black cottonwood series in the northwestern part and White
alder series in the southeastern part of the subsection. Sedge meadow
communities occur in wet areas.
Characteristic series by lifeform include:
Climate. The mean annual precipitation is about 30 to 60 inches;
much of it falls as snow. Mean annual temperature is about 45°
to 55° F. The mean freeze-free period is about 75 to 150 days.
Grasslands: Ashy ryegrass series, California oatgrass series,
Darlingtonia series, Idaho fescue series, Montane meadow habitat, Needle-and-thread
Shrublands: Birchleaf mountain-mahogany series, Bush chinquapin
series, Deerbrush series, Greenleaf manzanita series, Huckleberry oak series,
Interior live oak series, Mountain whitethorn 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, Jeffrey
pine series, Jeffrey pine - Ponderosa pine series, Mixed conifer series,
Ponderosa pine series, Red fir series, White fir series.