This coastal island covers approximately 14 acres and rises steeply 335 feet above sea level. The refuge provides an important sanctuary for Aleutian Canada geese and nesting seabirds. It is in fact known as the second largest nesting seabird colony south of Alaska (after the Farallon Islands).

The estimated number of seabirds using Castle Rock has been as high as 150,000. It also has the largest breeding population of common murres in California; the latest estimate for common murres was 98,000 in 1986. Aleutian Cackling Geese roost on the rock in the tens of thousands from mid-February through April.

Castle Rock Refuge also serves as a resting place for four species of pinnipeds, as well as harbor seals, northern elephant seals, California sea lions, and Stellar's sea lions.

Castle Rock Refuge is half a mile offshore from Crescent City in northern California. Bird watching is best with a spotting scope from Pebble Beach Drive pull out areas.

The refuge is a wildlife sanctuary and as such is closed to the public; it can be viewed from North Pebble Beach Drive in Crescent City.

Fees: No fees