Los Angeles County Department of Regional Planning - Geography

Geography

According to the 2000 census, the county has a total area of 4,752.32 square miles (12,308.5 km2), of which 4,060.87 square miles (10,517.6 km2) (or 85.45%) is land and 691.45 square miles (1,790.8 km2) (or 14.55%) is water. Los Angeles County borders 70 miles (110 km) of coast on the Pacific Ocean and encompasses towering mountain ranges, deep valleys, forests, islands, lakes, rivers, and desert. The Los Angeles River, Rio Hondo, the San Gabriel River and the Santa Clara River flow in Los Angeles County, while the primary mountain ranges are the Santa Monica Mountains and the San Gabriel Mountains. The western extent of the Mojave Desert begins in the Antelope Valley, in the northeastern part of the county. Most of the population of Los Angeles County is located in the south and southwest, with major population centers in the Los Angeles Basin, San Fernando Valley and San Gabriel Valley. Other population centers are found in the Santa Clarita Valley, Crescenta Valley and Antelope Valley.

The county is divided west-to-east by the rugged San Gabriel Mountains, filled with coniferous forests and subject to plentiful snowfall in the winter. The San Gabriel Mountains are part of the Transverse Ranges of southern California, and are contained mostly within the Angeles National Forest. Most of the highest peaks in the county are located in the San Gabriel Mountains, including Mount San Antonio (10,068 ft) at the Los Angeles-San Bernardino county lines, Mount Baden-Powell (9,399 ft), Mount Burnham (8,997 ft), and the well-known Mount Wilson (5,710 ft) where the Mount Wilson Observatory is located. Several smaller, lower mountains are located in the northern, western, and southwestern parts of the county, including the San Emigdio Mountains, the southernmost part of Tehachapi Mountains, and the Sierra Pelona Mountains.