San Mateo Rocks

San Mateo Rocks are uninhabited islands that lie approximately 0.5 mi off the coast of California, to the south of San Clemente, and just north of San Mateo Point, a minor headland that marks the border between Orange County and San Diego County. The rocks rise about 3 ft (or about 1 m) above high tide. In 2017 the San Mateo Rocks, a pinniped haul-out and scuba destination, became part of the California Coastal National Monument.

The Rocks first appear in the documentary record of the area in 1889, when they were described in the Coast Pilot. The sloop Victoria wrecked on the rocks in a storm in 1907. In 1931 the United States Coast Guard reserved the location (along with several other Orange County Rocks) for a possible future San Mateo Rocks Lighthouse, and an act of Congress assigned ownership to the Bureau of Land Management in 1935, but the lighthouse facility was never built. In the early 1970s the waters around the rocks were a collection site for seaweed species in genus Gelidium for use in agar production.

The rocks host a transient population of California sea lions. Indigenous people may have used San Mateo Rocks as a pinniped hunting ground. On one occasion this population of sea lions attracted a pod of orcas—quite uncommon in local waters—who used a clever pack-hunting technique to force the sea lions off the rock and into the water where they would be ready prey. The rocks are a common destination for local dive boats.