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Ecological Sections: Sierra Nevada - (MAP)

Subsection M261Eb
Fredonyer Butte - Grizzly Peak

This subsection extends from the northern edge of the Sierra Nevada, which is along the Susan River, south to Grizzly Peak.  It has a temperate to cold, subhumid to humid climate.  MLRA 22e.

Lithology and Stratigraphy.   Strongly folded basement rocks predominate in this subsection. They include metamorphosed Jurassic marine sedimentary, Jurassic-Triassic volcanic, and  Paleozoic marine sedimentary and volcanic rocks.  There are a few small Mesozoic granitic bodies.   Tertiary volcanic rocks, largely dacitic lahar, and nonmarine  sedimentary rocks are moderately extensive in the northern part of the subsection.  Quaternary alluvium has accumulated in Mountain Meadows and a few smaller valleys.

Geomorphology.   Steep mountain and moderately steep hill slopes predominate in this subsection.  Alluvial fans, floodplains, terraces, and basin floors are present but not extensive.  Keddie Ridge, one of the few mountains that is distinctly elongated, is aligned toward the west-northwest.  The elevation ranges from about 4000 feet along Lights Creek up to 7387 feet on Hamilton Mountain, 7472 on Dyer Mountain on Keddie Ridge, and 8197 feet on Grizzly Peak.  Faulting, mass wasting, and fluvial erosion are the main geomorphic processes.   The north sides of Grizzly Peak and Keddie Ridge were glaciated during the Pleistocene.

Soils.  The soils are mostly Ultic Argixerolls, Ultic Haploxeralfs, Ultic Palexeralfs, Andic Xerumbrepts; Pachic Haploxerolls; and a diverse group of shallow soils.  There are Aquolls in Mountain Meadows.  The soils are mostly well drained, some soils in meadows are poorly drained.  Soil temperature regimes are mesic and frigid.  Soil moisture regimes are mostly xeric, but aquic in Mountain Meadows.

Vegetation.   The predominant natural plant communities are Jeffrey pine series, Mixed conifer series, and White fir series.  Small areas of Red fir series occur at the highest elevations.  Western juniper series is present on some shallow soils.  The most common streamside riparian communities are Black cottonwood at lower elevations and Mountain alder series at higher elevations.  Sedge meadow communities occur in wet areas.

    Characteristic series by lifeform include:
    Grasslands: Ashy ryegrass series, Green fescue series, Idaho fescue series, Montane meadow habitat, Nebraska sedge series, Needle-and-thread series, Rocky Mountain sedge series.
    Shrublands: Bitterbush series, Greenleaf manzanita series, Parry rabbitbrush series, Rubber rabbitbrush series, Tobacco brush series.
    Forests and Woodlands: Aspen series, Incense-cedar series, Jeffrey pine series, Jeffrey pine - Ponderosa pine series, Mixed conifer series, Mountain juniper series, Ponderosa pine series, Red fir series, Western white pine series, White fir series.
Climate.  The mean annual precipitation is about 20 to 40 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 125 days.

Surface Water.  Runoff is rapid from most of the area, but slow on the basin floor in Mountain Meadows.  Most of the runoff flows to tributaries of the Feather River.  In the northern part of the subsection it flows to the Susan River, which runs to Honey Lake.   There is a reservoir on Mountain Meadows. 

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