Anacapa Island (from Anyapax, meaning "mirage, illusion") is a small volcanic island located about 11 miles off the coast of California. The island is composed of a series of narrow islets. The three main islets, East, Middle and West Anacapa, have precipitous cliffs, dropping off steeply into the sea.

Anacapa was formed by volcanic eruptions between 19 and 15 million years ago. Lava from these eruptions can be found across the region, and in depths of up to 10,000 feet. The rocks that make up Anacapa are composed of lava, breccias, volcanic ash, and cinders.

Erosion has heavily weathered the lava formations of Anacapa, and wave action caused the island to split into three islets in recent prehistoric times. The islets display a wide variety of erosional features including sea arches, sea caves, stacks, wave-cut platforms, surge channels, and blowholes.

In 1910, American naturalist and conservationist Charles Frederick Holder said of Anacapa:

"Arid appearing, desolate, wind-swept, Anacapa is withal a valuable possession to its owner, and one of the picturesque islands of the entire group. Its strange rocks, moving, passing, intermingling, made a strong impression on my mind, an impression of warring nature, conflicts of wind and rock, of seas eating into its very vitals, of caves that undermine it, and of the old rock fighting for its very life against the sea."

Anacapa Island provides a critical habitat for seabirds, pinnipeds such as California sea lions, and several endemic plants and animals. Great white sharks, feeding on pinnipeds, are found in the waters of the Channel Islands, including Anacapa. The island has a somewhat diverse flora, including around 150 native plants, including 16 endemics (two of which are unique to the island) plus many introduced species.

Raymond "Frenchy" LeDreau occupied four shacks on West Anacapa at Frenchy's Cove, living as a recluse for 30 years, departing the island in his eighties after the island had become a national monument. (Honestly, goals.)

The United States Lighthouse Service built an acetylene-powered light and whistling buoy in 1912 at the east end of the island, and constructed the East Anacapa Island Light between 1930 and 1932. It was the last lighthouse built by the Lighthouse Service on the California coast.

Frenchy's Cove was cleaned up starting in June 1959, and a permanent park ranger replaced the seasonal one in the mid-1970s.