The cities of Sacramento, Bakersfield, and Fresno are in the Central Valley. The valley has the Sierra Nevada to the east and the Pacific Coast Ranges to the west. It is California's single most productive agricultural region and one of the most productive in the world. It produces more than half the fruit, vegetables, and nuts grown in the United States. More than seven million acres (28,000 km) of the valley are irrigated by an extensive system of reservoirs and canals.