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Subsection M261Ab
Gasquet Mountain Ultramafics

This subsection encompasses ultramafic rocks in the Josephine ophiolite and from the Josephine ophiolite southward along the east side of a thrust fault that separates the Coast Range mountains from the Klamath Mountains.  It ends at Burrill Peak, just north of the Klamath River.  Marine air moderates the climate of most of the subsection.  It has a temperate and humid climate.  MLRA 5b.

Lithology and Stratigraphy.  This subsection is dominated by partially to completely serpentinized peridotite of a Jurassic-aged ophiolite, called the Josephine ophiolite.  Some gabbro and diabase are included in the subsection.
Geomorphology.  This is a subsection of mountains with rounded ridges, steep sides,  and narrow canyons.   Some of the mountains have broad summits.  Landslides are common, particularly where the peridotite has been completely serpentinized and sheared.  The elevation range is about 200 to 4800 feet.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Dystric Xerochrepts, Lithic Xerochrepts, Ultic Haploxeralfs, and Typic Haploxerults.  Kandihumults occur on broad mountain summits and mountain benches.  Grayer soils are in serpentinitic families and redder soils are in oxidic families.  Most of the soils are well drained, but some are poorly drained.  Soil temperature regimes are predominantly mesic.  Soil moisture regimes are xeric.

Vegetation.   The predominant natural plant communities are Jeffrey pine series and Lodgepole pine series.   Port Orford-cedar series is common on wet mountain sideslopes and along streams.  Douglas-fir series and Western white pine series occur on old land surfaces where most of the magnesium (Mg) has been leached from the soils.  Darlingtonia series is common in small bogs and fens.

Climate.   The mean annual precipitation is about 80 to 120 inches.  Most of the precipitation is rain at lower elevations, with some snow at higher elevations.  Mean annual temperature is about 46° to 57° F.  The mean freeze-free period is about 100 days at higher elevations to 225 days at lower elevations.

Surface Water.  Runoff is rapid.  It drains to the Smith River and tributaries of the Klamath River.  There are many wet spots, or bogs, on sloping to moderately steep mountain slopes where water seeps from the ground.  There are a few small lakes, and temporary ponding occurs on some landslides.

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