San Nicolas Island is the most remote of the Channel Islands, off of Southern California, 61 miles (98 km) from the nearest point on the mainland coast. It is part of Ventura County. The 14,562 acre island is currently controlled by the United States Navy and is used as a weapons testing and training facility, served by Naval Outlying Landing Field San Nicolas Island. The uninhabited island is defined by the United States Census Bureau as Block Group 9, Census Tract 36.04 of Ventura County, California. The Nicoleño Native American tribe inhabited the island until 1835. As of the 2000 U.S. Census, the island has since remained officially uninhabited, though the census estimates that at least 200 military and civilian personnel live on the island at any given time. The island has a small airport, though the 10,000 foot (3,000 m) runway is the second longest in Ventura County. Additionally, there are several buildings including telemetry reception antennas.

The Channel Islands are an eight-island archipelago located within the Southern California Bight in the Pacific Ocean, off the coast of California. They define the Santa Barbara Channel, which sits between the islands and the California mainland. The four Northern Channel Islands are part of the Transverse Ranges geologic province, and the four Southern Channel Islands are part of the Peninsular Ranges province. Five of the islands are within the Channel Islands National Park, and the waters surrounding these islands make up Channel Islands National Marine Sanctuary. The Nature Conservancy was instrumental in establishing the Channel Islands National Marine Sanctuary.