Chapter 31
Ecological Subregions of the United States



California Dry Steppe

One Section has been delineated in this Province:

The area of this Secion, which is located in California, is about 19,200 mi2 (49,700 km2).

Section 262A--Great Valley

Geomorphology. This low fluviatile plain is in the Great Valley geomorphic province. Elevation ranges from sea level to 800 ft (0 to 243 m).

Lithology and Stratigraphy. This area has Cenozoic nonmarine sedimentary rocks and alluvial deposits.

Soil Taxa. Soils include Alfisols, Entisols, Histisols, Inceptisols, Mollisols, and Vertisols, in combination with a thermic soil temperature regime and xeric, aquic, or aridic soil moisture regimes.

Potential Natural Vegetation. K\"uchler mapped vegetation as California prairie, riparian forest, tule marsh, San Joaquin saltbush and valley oak savanna. Predominant potential natural communities are Valley Oak, Valley Needlegrass, and Saltbush series.

Fauna. Former inhabitants include grizzly bear, wolf, tule elk, and pronghorn antelope. Much of the natural habitat has been modified throughout the Section. The Section contains wetlands that are important feeding and resting areas for migrating waterfowl. Many waterfowl species are year-round residents. Mammals include mule deer, black-tailed deer, coyote, muskrat, beaver, ground squirrel, cottontail, jack rabbit, kangaroo rat, and the endangered kit fox. Common birds include hawks, golden eagle, owls, white-tailed kite, quail, mourning dove, mockingbird, scrub jay, gulls, herons, crows, western meadowlark, finches, sparrows, roadrunners (southern part), and the introduced Chinese ringneck pheasant.

Climate. Precipitation ranges from 5 to 30 in (130 to 760 mm). Temperature averages 55 to 66 oF (13 to 19 oC). The growing season lasts 230 to 350 days.

Surface Water Characteristics. Many slow moving rivers flow to the delta east of San Francisco Bay via the Sacramento and San Joaquin River systems. Flows to these levied, alluvial channel river systems are regulated throughout the year by the many dams occurring in adjacent Sections. Constructed deep water ship channels also connect to Sacramento and Stockton. Many rivers and perennial streams flow west from the Sierra Nevada foothills Section to the Sacramento and San Joaquin Rivers. The many alluvial channels that flow eastward from the Coast Ranges to the Sacramento and San Joaquin Rivers are mostly dry during summer months; only a few are perennial streams. The southern part of the San Joaquin Valley drains to basins and does not reach the San Joaquin River.

Disturbance Regimes. Historic occurrence of fire has changed from frequent, fast moving, large fires to infrequent small fires, or fire has been mostly excluded because of conversion to irrigated agriculture and urban uses.

Land Use. Composition and successional sequence of some communities (especially grassland communities) has changed because of plant and animal species introduced between the early 1800's and early 1900's. These changes related to grazing, agriculture, and urbanization. Most of the Section is converted to irrigated agriculture. Rapidly expanding urbanized areas are scattered throughout the Section. Flood control has decreased the duration and extent of wetlands.

Cultural Ecology. Humans have been utilizing the central valley for 10,000 years, and have been an integral part of its ecology for 3,000 to 5,000 years. The valley contains some of the densest year-round prehistoric habitation locations in California, particularly along riparian areas. Intensive occupation, resource procurement and processing practices, and vegetation manipulation through the use of fire sometimes altered the riverine environment. Around the time of the Gold Rush, Euro-americans flooded into the valley, converting the land to agriculture, which became the mainstay of California economy. The river systems provided early transportation routes. Sacramento and Stockton are shipping ports served by deep water channels. Contemporary attitudes and beliefs are varied; lifestyles are both urban and rural; economies are dominated by agriculture, government, and services; populations are diverse.

Compiled by Pacific Southwest Region.