Castle Rock

This small offshore island and its adjacent reefs are second in importance in the State only to the Farallon Islands as a sea bird breeding ground. Approximately 25,000 pairs nest here between March and July. Common murres, Uria aalge, are the most abundant and the breeding colony here is the largest in the State. There are also major colonies of Cassin's auklet, Ptychoramphus aleutica, Leach's petrel, Oceanodroma leucorhoa, fork-tailed petrel, Oceanodroma furcata, pigeon guillemot, Cepphus columba, and the tufted puffin, Lunda cirrhata. Other breeding birds include the Western gull, Larus occidentalis, black oystercatcher, Haematopus bachmani, pelagic cormorant, Phalacrocorax pelagicus, and Brandt's cormorant, Phalacrocorax penicillatus.

A colony of rhinoceros auklets, Cerorhinca monocerata, numbering 150 pairs, bred here in 1969, the first recorded in California for the past hundred years.

Harbor seals, Phoca vitulina, use the island as a rookery. Steller sea lions, Eumetopias jubata, and California sea lions, Zalophus californianus, are also seen, and elephant seals, Mirounga angustirostris, have been recorded.

The vegetation is primarily grassland, including a Poa-Lasthenia association and a heavy stand of rye grass, Leymus mollis. Dudleya spp. are found on the rocks.

The island and reef lie approximately 1.6 kilometers (1 mile) south of Point Saint George, to which it is related geologically. In addition to the steep, Franciscan formation rocks, there is a sandy beach and a grassy flat and slope. The top soil of the flat and slope is at least 30 centimeters (12 inches) thick and honeycombed with burrows.

Integrity: There is no development, although there have been proposals for quarrying the island. It is in private ownership and the owners have protected it. It has been recommended that the State acquire it.

Use: Private

January 1975