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Ecological Sections: Sierra Nevada - (MAP)

Subsection M261Ed
Greenville - Graeagle

This 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.

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.

Photo: Subsection M261EdGeomorphology.   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.

Soils.  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.

Vegetation.  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:
    Grasslands: Ashy ryegrass series, California oatgrass series, Darlingtonia series, Idaho fescue series, Montane meadow habitat, Needle-and-thread series.
    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.
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.



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