Topanga is an unincorporated area in western Los Angeles County, California, USA. It is located in the Santa Monica Mountains and occupies Topanga Canyon. Topanga is 12,748 acres (52 km²) in size, and is bounded on three sides by State Park or conservancy lands, and on the south by the Pacific Ocean and a small strip of Malibu, which is the main community to the west. On the east is Pacific Palisades. Topanga has a population of 5,441 as of 2000. The ZIP code is 90290 and the area code is primarily 310, with 818 only at the north end of the canyon. It is in the 3rd County Supervisorial district.