Subsection M261Ak
Lower Scott Mountains

Lithology and Stratigraphy.  This subsection is dominated by ultramafic rocks of the Trinity terrane, which is a complex polygenetic assemblage of disrupted Cambrian, Ordivician, Silurian, and Devonian ocean crust that has been intruded by Mesozoic granitic rocks.  The terrane is represented by serpentinized peridotite, gabbro, diabase, and minor volcanic rock.  The granitic rocks are generally quartz diorite to slightly more silicic rocks.

Geomorphology.  This is a subsection of mountains with rounded summits, steep sides, and narrow canyons.  The elevation range is about 1500 to 5000 feet.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Typic and Lithic Xerochrepts and Mollic and Ultic Haploxeralfs. Ultic Palexeralfs occur on old land surfaces.  Soils on granitic rocks are mostly shallow Dystric Lithic Xerochrepts, Dystric Xerochrepts, and Ultic Haploxerolls.  The soils are well drained.  Soil temperature regimes are mesic.  Soil moisture regimes are xeric.

Vegetation.   The predominant natural plant communities are Jeffrey pine series on ultramafic rocks, Douglas-fir - ponderosa pine series on gabbro and diabase, and Mixed conifer series on granitic rocks.  Canyon live oak series occurs on  very steep rocky slopes with stony soils.

Characteristic series by lifeform include:
Grasslands: California annual grassland series, Purple needlegrass series.
Seeps: Darlingtonia series.
Shrublands: Brewer oak series, Greenleaf manzanita series, Wedgeleaf ceanothus series, Whiteleaf manzanita series.
Forests and woodlands: Black oak series, Canyon live oak series, Douglas-fir series, Douglas-fir - ponderosa pine series, Incense-cedar series, Jeffrey pine series, Knobcone pine series, Mixed conifer series, Oregon white oak series, Ponderosa pine series, Port Orford-cedar series.

Surface Water.  Runoff is rapid.  It drains mostly to the Trinity River on the west and to the Sacramento River on the east, and a small part of the subsection drains to the Shasta River on the northeast.  Larger streams are perennial and most smaller streams are dry by the end of summer.  There are no natural lakes in the subsection.