San Joaquin Valley, valley in central California, U.S., the southern part of the state’s vast Central Valley. Lying between the Coast Ranges (west) and the Sierra Nevada (east), it is drained largely by the San Joaquin River. The valley is one of the most productive agricultural regions in the United States; parts of it are under irrigation. The San Joaquin Valley is one of the principal locations in Californian John Steinbeck’s novel The Grapes Wrath (1939).