Soils

Soil is the base for the vegetation of any area. Ninety percent of the soils in the study area are fertile loams, so the dense vegetation found here is not surprising.

Five types of soils are found on or near Dog Island. The island itself is an alluvial soil known as Red Bluff loam. It consists of up to 15% gravel, and has both high available water and high moisture-holding capacity (USDA Soil Conservation Service 1967).

The low area to the north of the island is made up of the Columbia loam complex, ranging from mixed soils of silt and gravels to fine sandy loams. These soils generally lie above all but the highest floods, are well drained, and have moderate permeability. They are brown to pale brown in color and are neutral to slightly acid. These are very fertile soils, favored for farming (ibid .).

The soil in the sloping area to the south of Brewery Creek is an Arbuckle gravelly loam. It

is an easily channeled soil with poor waterholding characteristics, very slow permeability, and a clay substrate (ibid .).

Duncan Hill, the bluff on the northwest side, is made up primarily of Newville gravelly loam. This soil is yellowish-brown on the surface and is slightly acidic. The subsoil is a reddish-brown gravelly clay. It is made up of sediment from conglomerate and silt stone of the Tehama formation. In addition, a portion of the hill consists of a mixture of Corning-Redding gravelly loams, a medium acidic, reddish-brown soil with a red clay subsoil. This soil has low permeability and high runoff (ibid .).