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Subsection M261Ba
Eastern Franciscan

This subsection is in the higher elevation part of the northern California Coast Ranges that is far enough inland to have little oceanic influence on climate.  It has a temperate to cold, humid climate.  MLRA  5d.

Lithology and Stratigraphy.  This subsection is dominated by Jurassic and Cretaceous Franciscan metaclastic  rocks of the Eastern Belt.  They are intensely folded and faulted.  Ultramafic rocks are minor components in this subsection.

Geomorphology.  This is a subsection of mountains with rounded ridges, steep sides,  and narrow canyons.    Most of the mountains are elongated in north-northwest to northwest directions and have subequal summits with increasing elevation toward the interior.   The elevation range is from about 1200 feet up to 8092 feet on Mt. Linn in the South Yolla Bolly Mountains.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Dystric Xerochrepts, Dystric Lithic Xerochrepts, and Lithic Xerorthents.  At higher elevations, Typic and Lithic Xerumbrepts are most common.  The soils are leached free of carbonates.  Few surfaces are old enough, because of active erosion, to have Alfisols or Ultisols.  Soil temperature regimes are predominantly mesic, some frigid, and minor cryic.  Soil moisture regimes are almost exclusively xeric.

Vegetation.   The predominant natural plant community is Mixed conifer series, except in the northern part of the subsection where Douglas-fir - tanoak series is the predominant plant community.  Red fir series and White fir series are common in areas of frigid soil temperature regimes.

Characteristic series by lifeform include:

Climate.   The mean annual precipitation is about 40 to 120 inches.  Most of the precipitation is rain at lower and snow at higher elevations.  Mean annual temperature is about 35° to 55° F.  The mean freeze-free period is in the range from 100 days at higher elevations to 200 days at low elevations.

Surface Water.  Runoff is rapid and all but the larger streams are dry through much of the summer.  There are a few small lakes and wet meadows in glacial basins at higher elevations.


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