California's geography is rich, complex, and varied. In the middle 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. The water supply for much of the state is provided by the State Water Project. The Central Valley Project supports some municipal water supplies, though it primarily provides water to irrigated agriculture. With dredging, several 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 a major estuary that supports a brackish ecosystem while serving as the water supply hub for much of the state's population. The Channel Islands are located in the southern part of the state, stretching from Santa Barbara to Orange County. These islands have few inhabitants, but the northernmost islands are a national park. They and the largest island, Santa Catalina Island are attractive to visitors.

In the center and east of the state are the Sierra Nevada (meaning Snowy Range in Spanish), which include the highest peak in the contiguous 48 states, Mount Whitney, at 14,505 feet (4421 m). Also located in the Sierra are the world-famous Yosemite National Park and a deep freshwater lake, Lake Tahoe, the largest lake in the state by volume. To the east of the Sierra are Owens Valley and Mono Lake, an essential seabird habitat. To the west is Clear Lake, California's largest freshwater lake by area. The Sierra Nevada reaches arctic temperatures in the winter and has several dozen small glaciers, including the most southern glacier in the United States (Palisade Glacier).

About 35% of the state's total surface area is covered by forests. California's diversity of pine species is unmatched by any other state. Though other states have a higher percentage of their land area covered by forests, in terms of total area, California contains more forestland than any other state except Alaska. Most of the forest is found in 2 areas: the northwestern part of the state and along the western slope of the Sierra Nevada. Smaller forests, mainly consisting of oaks, can be found along the coast ranges of California closer to the coast, and also in the foothills of the Sierra Nevada. Smaller areas of pine forests can be found in the San Gabriel and San Bernardino mountains of Southern California and also in the mountain areas of central San Diego County. Deserts in California make up about 25% of the total surface area. In the south lay the Transverse Ranges and a large salt lake, the Salton Sea. The south-central desert is called the Mojave. To the northeast of the Mojave lies Death Valley, which contains the lowest, hottest point in North America, Badwater Flat.

Along the densely populated and long California coast are several major metropolitan areas, including San Jose-San Francisco-Oakland, Los Angeles-Long Beach, Santa Ana-Irvine-Anaheim, Riverside-San Bernardino, California and San Diego. Climates near the Pacific Ocean are remarkably moderate compared with inland climates. Winter temperatures seldom reach freezing and summer temperatures rarely reach above the high 80's Fahrenheit (low 30's Celsius).

California is famous for earthquakes due to the presence of a number of faults, in particular the San Andreas Fault. While powerful earthquakes in the United States have occurred in other states such as Alaska, Washington, Oregon, and Missouri (along the New Madrid fault), people are more aware of California's earthquakes due to their frequency and tendency to strike in highly populated areas.

California is also home to several volcanoes, some active such as Mammoth Mountain. Other volcanoes include Lassen Peak, which erupted from 1914 and 1921, and Mount Shasta.

The region was inhabited by Native Americans before European explorers started to make sporadic visitations during the 16th Century. California had the highest density and greatest diversity of indigenous peoples in what is now the United States. Spain colonized the coastal areas of the territory starting in 1769. As a result of the Mexican War of Independence, California became a part of the Mexican Republic in 1821. It was subsequently captured by the United States in the Mexican-American War (1846-1848) which was concluded with the Treaty of Guadalupe Hidalgo. The California Gold Rush of 1848-1849 brought about 90,000 additional U.S. immigrants into the state, and California became the 31st state of the Union in 1850.

Although the state's sunny climate has given it a historic reputation for being laid back compared to the East Coast, the $1.55 trillion (as of 2005) California economy is larger than all but the top 7 national economies in the world and is responsible for 13% of the United States' $13 trillion gross domestic product (GDP). The state's major predominant industries include agriculture, entertainment, light manufacturing, and tourism. California is also the home of several significant economic regions such as Hollywood (entertainment), the California Central Valley (agriculture), Silicon Valley (computers and high tech), and the Wine Country (wine).

The Governor of California and the other state constitutional officers serve four-year terms and may be re-elected only once. The California State Legislature consists of a 40 member Senate and 80 member Assembly. Senators serve four year terms and Assembly members two. The terms of the Senators are staggered so that half the membership is elected every two years. The Senators representing the odd-numbered districts are elected in years evenly divisible by four, which corresponds to presidential election years. The Senators from the even-numbered districts are elected in the intervening even-numbered years, in the gubernatorial election cycle. California's legislature is organized in such that the party caucus leaders wield great power and can usually speak on behalf of their caucuses. Many important legislative decisions are thus not made on the floor of the legislature but in back-room deals by the "Big Five," which comprises the governor and the Democratic and Republican leaders of each chamber. Members of the Assembly are subject to term limits of 3 terms, and members of the Senate are subject to term limits of 2 terms.