Among California's eight national parks are some of the most frequently visited parks in the country. Yosemite National Park covers about 3100 sq. km (about 1200 sq. mi) of scenic wild lands, including alpine wilderness, three groves of giant sequoias, and the glacially carved Yosemite Valley, with its impressive waterfalls, cliffs, and unusual rock formations. Sequoia National Park, located in central California, is home to the 84-m (275-ft) General Sherman giant sequoia, considered the most massive tree in the world. Its circumference measured directly above the ground flare is 25 m (83 ft). Some of the world's tallest trees grow in the Redwood National Park in the northwestern portion of the state. Joshua Tree National Park has a representative stand of Joshua trees and other desert vegetation. More of California's dramatically beautiful landscapes can be found in Kings Canyon National Park, located in the Sierra Nevada and containing two enormous canyons of the Kings River. In a stark contrast is Death Valley National Park, which encompasses the lowest land surface in the western hemisphere and the place where the country's record high temperature was recorded.

Before the 1980 eruption of Mount Saint Helens in Washington, Lassen Peak, located in Lassen Volcanic National Park, was the most recently active volcano in the contiguous 48 states. Other signs of volcanic activity, including cinder cones, lava flows, lava tube caves, pit craters, and steam vents, can be found in Lava Beds National Monument, near the Oregon border, and in the Mammoth Mountain area of the eastern Sierra Nevada. Devils Postpile National Monument, also near Mammoth Mountain, contains lava columns up to 18 m (60 ft) high, and Pinnacles National Monument, in the Diablo Range, has rock spires, caves, and a variety of volcanic features.

Five of the eight islands in the Santa Barbara channel comprise the Channel Islands National Park. A portion of the park is under water and provides habitat for marine life ranging from microscopic plankton to the world's largest creature, the blue whale. Also preserving a section of California's coastal environment is Point Reyes National Seashore about 60 km (about 40 mi) north of San Francisco.

Other national sites commemorate the rich history of California. Cabrillo National Monument in San Diego's Point Loma district marks the spot where in 1542 Europeans first set foot upon what is now California. Fort Point National Historic Site, which is part of Golden Gate National Recreation Area, contains the fort built in the mid-1800s to prevent any hostile fleets from entering San Francisco Bay. San Francisco Maritime National Historical Park contains a square-rigged sailing ship, steam schooner, three-masted schooner, steam tug, and a paddle wheel tug.

Manzanar National Historic Site, located in the southern Owens Valley of eastern California, commemorates the internment beginning in 1942 of Japanese Americans during World War II. The area from Manzanar south through the Alabama Hills to Lone Pine with the highest part of the Sierra Nevada as a backdrop is one of the most popular film-making locations in the world, and now hosts the Lone Pine Film Festival every October.

Eugene O'Neill National Historic Site, in Danville, commemorates the only Nobel Prize winning playwright from the United States and the architect of modern American theater.

One of the country's earliest crusaders for national parks is remembered in two parks in California. John Muir National Historic Site, in Martinez, preserves the mansion where the naturalist lived. Also recognizing the explorer is Muir Woods National Monument, in Marin County, a peaceful grove of coastal redwoods.

The 18 national forests in California are administered by the United States Forest Service. National forests cover about 8.3 million hectares (about 20.6 million acres). Within the national forests are a number of wilderness areas and wildlife refuges. Los Padres National Forest, the largest national forest wholly within the state, covers about 708,000 hectares (1.7 million acres) in western California. Most of the other larger national forests in California lie in the northern and northeastern parts of the state. Shasta-Trinity national forest, in northern California, lies in a volcanic area culminating in the beautiful snowcapped Mount Shasta. In the northern coastal uplands is Six Rivers National Forest, noted for its groves of redwoods. Extending across the Sierra Nevada along California's eastern border are Plumas, Tahoe, Eldorado, Stanislaus, and Inyo national forests. Sierra National Forest, in the Sierra Nevada region, preserves stands of giant sequoias..