The island of San Nicolas is 61 miles from the coast, and has a total area of 22 square miles. The island is roughly a plateau, with arroyos cutting down to the shoreline. The eastern end of San Nicolas is a continually shifting area of sand that is thought to have varied greatly in size over the last hundred years. Land's End, the westernmost point of the island, is a haven for tide-pool life, sustaining such things as purple sea urchins, sea lettuce, snails, and anemones. Two lava reefs range westward from this area, and are abundant in lobster, abalone, and scallop beds. South of Land's end, sea lions bask on the lava ridges, and elephant seals keep a rookery as well.

Although at one time the island of San Nicolas supported a sizable human population, it has since been overgrazed by sheep and goats, making large extended habitation impossible. In 1933, the United States Navy assumed control of the island, and has since used it for gunnery practice, and as a monitoring site for the Pacific Missile Test Center. The island was named San Nicolas due to it's discovery on December 8th, which is the day of Saint Nicolas.