Watershed
At 31,800 sq mi (82,000 km2), the San Joaquin watershed drains a fair swath of inland central California, covering an area nearly the expanse of South Carolina. This includes the 15,600 sq mi (40,000 km2) San Joaquin basin proper, and the 16,200 sq mi (42,000 km2) Tulare Basin, each comparable to the size of the Upper Peninsula of Michigan. This makes it the largest single river basin entirely in the state. The San Joaquin River basin is roughly synonymous with the San Joaquin Valley, and is bounded by the Sierra Nevada to the east, the Coast Ranges on the west, and the Tehachapi Mountains on the south.
The watershed's major southeast-northwest axis runs roughly parallel with the Pacific coast of California; it measures 280 by 115 mi (450 by 185 km) covering all or parts of seventeen California counties (through which the river flows seven) stretching from north of Lodi to well south of Bakersfield. Most of the elevation change in the San Joaquin occurs within the first 97 mi (156 km) above Friant Dam. Its highest headwaters are at over 12,000 ft (3,700 m), but by the time the river reaches the foothills, it is a mere 580 ft (180 m) above sea level.
On the west and northwest, the San Joaquin watershed borders those of rivers draining into the Pacific, while beyond almost all of the other divides lie endorheic basins, mostly of the Great Basin. To the north, a low series of ridges separates the San Joaquin River basin from that of the Sacramento River. The Coast Ranges bound the watershed on the west and borders on the drainages of the Pajaro River, Salinas River and the endorheic Carrizo Plain. On the south, the Tehachapis wall off the San Joaquin Valley from the Mojave Desert. To the east, the Sierra Nevada separate the San Joaquin drainage from those of multiple smaller rivers that terminate in various Great Basin lakes. From north to south, these are the Carson, Walker, and Owens Rivers.
The overwhelming majority of the economic base in the San Joaquin River watershed is provided by agriculture. The valley is widely considered one of the most productive farming regions in the world, and the top four U.S. counties ranked by agricultural production are all located in the San Joaquin watershed and Tulare Basin. The crops grown in these four counties alone are valued at over $12.6 billion annually, while the production of the entire valley is estimated at more than $14.4 billion. The main crop in the valley by annual sales is cotton, but more than 200 types of produce are grown along the San Joaquin River and in the Tulare Basin, including rice, almonds and lettuce. Livestock raising is also a major business in the valley. This prodigious output has earned the basin many names, including the "breadbasket" or "salad bowl" of the United States.
As of 2009, the San Joaquin River watershed had a human population of roughly 4,039,000, about 1.9 million of whom live within the section of the watershed not including the Tulare Basin. The largest cities are Bakersfield, near the south end of the valley on the Kern River; Fresno, roughly in the geographic center; Modesto, on the Tuolumne River; and Stockton, on the southeast fringe of the Delta region. Other major cities include Visalia, Tulare, Hanford, Porterville, Madera, Merced, Turlock, Manteca and Lodi. Population growth is among the highest in the state of California and more than twice the U.S. average. In Madera County, near the geographic middle of the basin, growth was 51.5% between 1990 and 2003, the highest in the San Joaquin basin. Most of the major cities lie on the State Route 99 corridor, which runs along the entirety of the San Joaquin Valley and forms the primary thoroughfare for the valley. Interstate 5 provides the major transportation route for the west side of the valley.
Land cover in the watershed is predominantly agriculture and forest, and large expanses of shrubland and semiarid foothill terrain also occupy portions of the basin in addition to a growing urban percentage. Irrigated land covers 30% of the watershed followed by forested areas in addition to national forest and park land that encompass 26.8% of the total land area. Built-up areas use a much smaller percentage of the watershed, at just 1.9%. In the San Joaquin's direct drainage region (not including the Tulare Basin) agricultural cover was 19.2%, forests embraced 28.4%, and urban areas occupied 2.4% as of 1995. The basin's main population centers are in the north and south and population density generally increases from west to east. In fact, despite the relatively small percentage of developed areas, more than 50% of the population lives in the watershed's four largest cities: Fresno, Bakersfield, Stockton and Modesto.
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