Central California Valley
Flat, intensively farmed plains with long, hot dry summers and mild winters distinguish the Central California Valley from its neighboring ecoregions that are either hilly or mountainous, forest or shrub covered, and generally nonagricultural. It includes the flat valley basins of deep sediments adjacent to the Sacramento and San Joaquin rivers, as well as the fans and terraces around the edge of the valley. The two major rivers flow from opposite ends of the Central Valley, flowing into the Delta and into San Pablo Bay. It once contained extensive prairies, oak savannas, desert grasslands in the south, riparian woodlands, freshwater marshes, and vernal pools. More than half of the region is now in cropland, about three fourths of which is irrigated. Environmental concerns in the region include salinity due to evaporation of irrigation water, groundwater contamination from heavy use of agricultural chemicals, wildlife habitat loss, and urban sprawl. (USEPA 2013)
Central California Valley
Occurring in the central part of California, it differs from adjacent ecoregions that are hilly or mountainous, forest- or shrub-covered, and generally nonagricultural.
The ecoregion has a mild mid-latitude Mediteranean climate, bordering on a mid-latitude desert climate in the south. The region has long, hot dry summers and mild, slightly wet winters. The mean annual temperature is approximately 15°C to 19°C. The frost-free period ranges from 240 to 350 days. The mean annual precipitation ranges 125 mm in the south to 760 in the northern margins.
Once had extensive grasslands and prairies with a variety of bunchgrasses, perennial and annual grasses, and forbs. Most natural vegetation has been greatly altered. Some valley oak savanna Riparian woods of oak, willow, western sycamore, and cottonwood. Tule marsh; upper San Joaquin Valley has saltbush, iodinebush, and saltgrass.
Low gradient perennial and intermittent streams. Some large rivers, San Joaquin and Sacramento, are fed by rivers flowing west from the Sierra Nevada (6.2.12). Streams flowing eastward from coastal mountain ranges in Ecoregion 11.1.1. are mostly intermittent, dry during summer months. Extensive delta in the middle of the valley where the two large rivers converge. Some vernal pools, marshes, and wetlands. Extensive water diversions, channelization, and draining.
Mostly flat fluvial plains and terraces, a few low or rolling hills. Deep, marine and non-marine sedimentary deposits of clays, sands, silts, and gravels. Elevations range from sea level to about 210 m. A wide variety of soil orders occur including Alfisols, Aridisols, Entisols, Mollisols, and Vertisols. They have thermic soil temperature regime and aridic and xeric soil moisture regimes. They are generally deep, well-drained and loamy or clayey.
Pronghorn, Tule elk, mule deer, coyote, San Joaquin Valley kit fox, cottontail rabbit, jackrabbit, California ground squirrels, kangaroo rats, wintering waterfowl, yellow-billed magpie, Nuttall’s woodpecker, giant garter snake, chinook salmon, delta smelt.
Land Use/Human Activities
Extensive agriculture. Nearly half of the region is in cropland, about three fourths of which is irrigated. Major crops include rice, almonds, apricots, olives, grapes, cotton, citrus, and vegetables. Some dairy and cattle feedlots. Oil and gas production. Environmental concerns in the region include salinity due to evaporation of irrigation water, groundwater contamination from heavy use of agricultural chemicals, wildlife habitat loss, and urban sprawl. Larger cities include Redding, Chico, Davis, Sacramento, Stockton, Modesto, Merced, Fresno, and Bakersfield.
US Environmental Protection Agency. 2013. Primary distinguishing characteristics of level iii ecoregions of the continental united states. https://www.epa.gov/eco-research/level-iii-and-iv-ecoregions-continental-united-states