At the edge of the Pacific Ocean, the beach at Schooner Gulch State Beach near Mendocino looks as though it’s been scattered with oversized bowling balls. Almost perfectly spherical about two or three feet in diameter, stones like these have caused wild speculation wherever they’ve been discovered, with answers from aliens to dinosaurs, but the answer is actually simple geology.
Best observed at low tide, the so-called bowling balls are actually a geological phenomenon known as “concretion,” sedimentary rock formed by a natural process wherein mineral cements bind grains of sand or stone into larger formations. These boulders are the result of millions of years of concretion and erosion, exposing the hard spheres as the mudstone of the cliffs receded around them.
Although rare, this same phenomenon is what created the extraordinary Moeraki Boulders and Koutu Boulders in New Zealand, Cannonball River in North Dakota, Valley of Balls in Kazakhstan, as well as elsewhere in the world.
A peculiar story stands behind the Schooner Gulch name. The story has it that one night a schooner was stranded on the beach, but the following morning visitors could find no evidence of the vessel on the beach.
Know Before You Go
Schooner Gulch Beach is three miles south of Point Arena on California Highway 1. From Gualala, go north on Highway 1 until Mile Marker 11.41 where you can park on the west side of the highway facing south on the designated area for Schooner Gulch State Beach. You will find two trails from the parking area.At high tide, the bowling balls are likely to be covered by water and the walk along the beach may be difficult or even impossible. Thus, plan the trip accordingly.