California borders the Pacific Ocean, Oregon, Nevada, Arizona, and the Mexican state of Baja California. The state has strikingly beautiful natural features, including an expansive central valley, tall mountains, hot deserts, and hundreds of miles of scenic coastline. With an area of 411,000 km² it is the third largest state in the U.S and larger than Germany in size. Most major cities are at or near the Pacific coastline, notably Los Angeles, San Francisco, San Jose, Long Beach, Oakland, Santa Ana/Orange County, and San Diego. However, the capital, Sacramento, is in the Central Valley.

California has extremely varied geography. In the center of the state lies the California Central Valley, a huge, fertile valley bounded by the coastal mountain ranges in the west, the granite Sierra Nevada to the east, the volcanic Cascade Range in the north and the Tehachapi Mountains in the south. Mountain-fed rivers, dams, and canals provide water to irrigate the Central Valley. Water supply for much of the state, particularly the more populous cities in Southern California, is provided by the State Water Project. The Central Valley Project also provides municipal water supply, though it primarily provides water supply to irrigated agriculture. With dredging, several of these rivers have become sufficiently large and deep that several inland cities, notably Stockton, are seaports. The hot, fertile Central Valley is California's agricultural heartland and grows a large portion of America's food, yet near freezing temperatures are not uncommon during winter which sometimes wipe out portions of crops. The southern part of the valley, which is part desert, is known as the San Joaquin Valley (drained by the San Joaquin River), while the northern half is known as the Sacramento Valley (drained by the Sacramento River). The Sacramento-San Joaquin Bay Delta is major estuary that supports a brackish ecosystem, while serving as the water supply hub for much of the state's population.