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California's Central Valley is a large, flat valley that dominates the geographical center of the U.S. state of California. It is 40 to 60 miles (60 to 100 km) wide and stretches approximately 450 miles (720 km) from north-northwest to south-southeast, inland from and parallel to the Pacific Ocean coast. It covers approximately 22,500 square miles (58,000 km2), about 13.7% of California's total land area (slightly smaller than the state of West Virginia), and is home to some of California's most productive agricultural areas.

The Central Valley comprises multiple major watershed systems: the Sacramento Valley, which receives well over 20 inches (510 mm) of rain annually, in the north, and the drier San Joaquin Valley in the south, with the Tulare Basin and its semi-arid desert climate at the southernmost end. The Sacramento and San Joaquin river systems drain their respective valleys and meet to form the Sacramento-San Joaquin River Delta, a large expanse of interconnected canals, stream beds, sloughs, marshes and peat islands. The delta empties into the San Francisco Bay, and then ultimately flowing into the Pacific. The waters of the Tulare Basin essentially never flow to the ocean, though they are connected by man-made canals to the San Joaquin and could drain there again naturally if they were ever to rise high enough.

The valley encompasses all or parts of 18 Northern California counties: Butte, Colusa, Glenn, El Dorado, Fresno, Kings, Madera, Merced, Placer, San Joaquin, Sacramento, Shasta, Stanislaus, Sutter, Tehama, Tulare, Yuba, Yolo, and the Southern California county of Kern.

en.wikipedia.org/wiki/Central_Valley_(California)