Subsection M261Ac
Oregon Mountain

Lithology and Stratigraphy.  This subsection is dominated by Paleozoic metavolcanic rocks of the Salmon Hornblende Schist, and metasedimentary and metavolcanic rocks of the  Abrams Mica Schist, or Grouse Ridge Formation, that are between the Bully Choop fault on the east and the Siskiyou fault on the west.  The age of metamorphism is Devonian, which is when the Bully Choop fault was active.  Oregon Mountain is an outlier, or klippe, of metamorphosed marine sedimentary rocks from the Eastern Klamath Belt.  There are small areas of Lower Cretaceous marine sedimentary rocks of the Great Valley sequence and Oligocene nonmarine sedimentary rocks of the Weaverville formation.

Geomorphology.  This is a subsection of mountains with rounded ridges, steep sides, and narrow canyons.   There is a narrow floodplain and discontinuous terraces along the Trinity River and its tributaries.  The elevation range is from about 1500 feet up to 6974 feet on Bully Choop.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Typic, Dystric, Lithic, and Dystric Lithic Xerochrepts; Ultic Haploxeralfs; and, on older surfaces, Ultic Palexeralfs.  Soils on the nonmarine sedimentary deposits are mostly Mollic Haploxeralfs.  The soils are well drained.  Soil temperature regimes are predominantly mesic, with frigid and some cryic at higher elevations.  Soil moisture regimes are xeric.

Vegetation.   The predominant natural plant communities are Douglas-fir - ponderosa pine series and Mixed conifer series.  Canyon live oak series is common on very steep rocky slopes with stony soils.  White fir series, and some Red fir series,  occurs at higher elevations.

Characteristic series by lifeform include:
Grasslands: California annual grassland series.
Shrublands: Brewer oak series, Bush chinquapin series, Chamise series, Chamise - wedgeleaf ceanothus series, Greenleaf manzanita series, Holodiscus series, Huckleberry oak series, Tobacco brush series, Wedgeleaf ceanothus series, Whiteleaf manzanita series.
Forests and woodlands: Blue oak series, Birchleaf mountain-mahogany series, Black oak series, Canyon live oak series, Douglas-fir series, Douglas-fir - ponderosa pine series, Foothill pine series, Interior live oak, Ponderosa pine series, Red fir series, Valley oak series, White alder series, White fir series.

Surface Water.  Runoff is rapid.  It drains to the Trinity River and its tributaries, except southeast of Bully Choop where runoff drains to tributaries of the Sacramento River.  Larger streams are perennial and smaller ones are mostly ephemeral.  There are no natural lakes in the subsection.