CA Water Regions

The North Coast Hydrologic Region - This area extends from Tomales Bay (north of San Francisco) to the Oregon border, and inland primarily to the crest of the coastal watersheds. Major topographical features include the Klamath Mountains, the Coast Range, and the high plateau area of Modoc County. Rivers include the Klamath, Smith River, Mad River, and the Russian River. Lakes include Clear Lake Reservoir, Tule Lake, Lower Klamath Lake, and Trinity Lake. Land use is primarily in forest or rangeland, as well as some irrigated agriculture. Precipitation measures from 10 inches in the Klamath River Basin to more than 100 inches of rain per year in higher elevations. Cities include Crescent City, Eureka, Yreka, Ukiah, and Santa Rosa.

San Francisco Bay Hydrologic Region – This region extends from southern San Mateo County north to Tomales Bay, and inland to the area where the Sacramento and San Joaquin Rivers meet. Major topographical features include the Coast Range, the San Francisco, Suisun, and San Pablo Bays, the Santa Cruz Mountains, and the Diablo Range. Lakes in the area are San Andreas Lake and Crystal Springs Reservoir, which are both sag ponds along the San Andreas Fault trace. Land use is overwhelmingly urban, with such cities as San Francisco, Oakland, and San Jose. Wine grapes, artichokes, and flowers are agricultural crops. Rainfall ranges from 13 inches in Pittsburg to 48 inches at Kentfield.

Central Coast Hydrologic Region – The section limits are from Southern San Mateo County in the north, to Santa Barbara County in the south, and inland to the valleys. Landforms of interest are Monterey and Morro Bays, the Coast Range, the coastal plain of Santa Barbara County, and the inland valleys of Pajaro, Salinas, Carmel, Santa Maria, Santa Ynez and Cuyama. The urban landscape contains the cities of Santa Cruz, Salinas, Monterey, Paso Robles, San Luis Obispo, Santa Maria, and Santa Barbara. Precipitation ranges from 10 inches in the southern valleys to 50 inches in the mountains. Irrigated agriculture use is developed in the valleys, primarily with vegetable crops and such specialty crops as flower seeds (in Lompoc).
South Coast Hydrologic Region – Welcome to megalopolis, a highly urbanized area stretching from Northern Ventura County south to the Mexican border, and east to the San Gabriel, San Bernardino, and San Jacinto mountains. The cities of Ventura, Los Angeles, Long Beach, Santa Ana, San Bernardino, Big Bear Lake are among the many urban areas in this section of the state that contains moderate sized mountains, inland valleys, and coastal plains. Precipitation amounts are from 10 in the valleys and coastal areas to 45 inches in the mountains. The Santa Clara River, Sespe Creek, the Los Angeles River, the San Gabriel River, and the Santa Ana River are among the area’s hydrologic features. These are not the flowing rivers of the north coast, however. Many of these rivers have been channelized and concreted, and are far different than their natural form. These are low-volume flow rivers, rather seasonal, running at their highest after mountain snow melts, with contributory water from wastewater treatment plants, irrigation runoff, and street runoff. Most lakes in this area are actually reservoirs, made to hold water coming from the State Water Project, the Los Angeles Aqueduct, and the Colorado River Aqueduct. These reservoirs include Lake Casitas, Castaic Lake, Big Bear Lake, Lake Mathews, and Morena Lake. While most land use is urban, other land uses include national forest and a small percent is in irrigated crop acreage.

Sacramento River Hydrologic Region – This is the drainage area of the Sacramento River. The watershed encompasses area from the Oregon border (near Goose Lake) south to Collinsville in the Delta area, east to the crest of the Sierras, and west to the crest of the Coast Range. The Sacramento River is the largest river in the state. There are many rivers in this drainage basin, including the American River, the Bear River, the Yuba River, Feather River, and the Pit River. Lakes in this section are Goose Lake, Shasta Lake, Lake Almador, Lake Oroville, Clear Lake, Lake Berryessa, and Folsom Lake. Sacramento, Yuba City, Oroville, Chico, and Redding are major urban areas. While urban growth is occurring rapidly, the area is still intensively farmed. Irrigated acreage crops include rice, pasture, grain, fruits, nuts, and tomatoes. Precipitation ranges from 18 inches in the Central Valley to 80 inches in the Sierras, with much of that precipitation falling as snow.

San Joaquin River Hydrologic Region – The Delta, the Cosumnes River, and the San Joaquin River watershed are in this hydrologic region. Rainfall amounts are from 9 inches in the southern area to 17 inches in the north. This is a region of dammed Sierran Rivers. The rivers are the Fresno, Chowchilla, Merced, Tuolumne, Stanislaus, Mokelumne, and the Cosumnes. The reservoirs on these rivers are Hensley Lake, Eastman Lake, Lake McClure, New Don Pedro Lake, New Melones Lake, Camanche Reservoir, and Jenkinson Lake. Urban centers include Lodi, Stockton, Tracy, Modesto, Turlock, Merced, and Madera. Agriculture is expected to decrease due to urban encroachment of San Francisco commuters. Crops that are grown in the region are alfalfa, corn, cotton, fruit, nuts, and grapes.

Tulare Lake Hydrologic Region – This region is bounded on the north by the San Joaquin River watershed, on the south by the Tehachapi Mountains, on the east by the Sierra Nevada range, and on the west by the Temblor Range. Most of the population is on the milder, less arid east side of the valley, including towns such as Bakersfield, Visalia, Fresno, Clovis, Tulare, and Delano. Rivers are the Kings, Kaweah, Tule, and Kern, with reservoirs Pine Flat Lake, Lake Kaweah, Success Lake, and Isabella Lake. With no outlet to the sea, the area naturally drains to the Tulare, Buena Vista, and Kern Lakebeds, which were drainage sinks. These areas have been converted to agriculture. Rainfall in the valley varies from 6 to 11 inches a year, to mountain precipitation of 12 to 36 inches. An agriculturally important area, produce includes grapes, almonds, pistachios, alfalfa, grain, and corn. Other land uses are industrial, most notably oil production in the southwest valley in the Taft-McKittrick area.

North Lahonton Hydrologic Region – This area is comprised of a ribbon of land on the east border of California, stretching from the Oregon border southward to the Lassen area, continuing south to Lake Tahoe, and still hugging the eastern boarder to its southern boundary which includes the Walker River drainage basin. Precipitation in this high desert to alpine region averages from 8 inches in the valleys to more than 70 inches in the mountains. This is not an urbanized area. The largest population can be found in Susanville, with other populated areas including Lake Tahoe and Truckee. Land use is primarily in cattle ranching, as the more extreme climate makes for a limited growing season for agriculture. Pasture and alfalfa are the primary crops. Other land uses are forest and recreational lands. Lakes include Lake Tahoe, Honey Lake, Eagle Lake, and Upper Lake. Rivers are the Truckee, Carson, and Walker.

South Lahonton Hydrologic Region – Hugging the eastern California border with Nevada, this region is bounded on the north to Mono Lake, the west to the crest of the southern Sierra Nevada mountains, and the south to the San Gabriel mountains. Topographic features include the Owens Valley, Death Valley, and Mount Whitney (elevation 14,495 feet). There are many playas (dry lakebeds) and drainage sinks. Rivers include the Owens and Mojave, as well as the intermittent Amargosa River. There are few lakes in this desert area. The ones that do exist include Mono Lake, Lake Crowley, Haiwee Reservoir, and Silverwood Lake. Annual rainfall ranges between 4 to 10 inches in the valley, and up to 50 inches in primarily snow in the Sierras. Urban areas include Lancaster, Palmdale, Victorville, Hesperia, Bishop, Barstow, Lone Pine, and Mammoth Lake. 75 percent of the land in this region is considered public land. There is little irrigated cropland, mainly pasture and alfalfa.

Colorado River Hydrologic Region – In the southeast part of the state is the Colorado River region. The eastern boundary is the Nevada state line, along with the Arizona state line – which is formed by the Colorado River. To the north, the region is bounded by the southern edge of the Mojave River watershed in the Victor Valley. The western boundary is the crest of the San Bernardino, San Jacinto, Santa Rosa, and Peninsular Ranges. The southern boundary is the border with Mexico. Geographic interests include volcanic craters, sand dunes, the San Andreas Fault, and the Salton Trough. Rivers include the Colorado, the New River, and the Alamo River. The only lake is the Salton Sea. Population centers include Palm Springs, Indio, El Centro, Calexico, Beaumont, Needles, and Blythe. This is a largely agricultural area, with crops planted in alfalfa, winter vegetables, melons, grapes, and dates. Other land uses include resorts, campgrounds, and tourist destinations.

All of this information and more can be found in the California Water Plan Update, 1998.