The Little River Punchbowl is a littoral sinkhole near Little River, about 3.3 miles (5.3 km) northwest of Albion and 2.7 miles (4.4 km) south-southeast of Mendocino, California. This large, forested pit formed when a sea cave collapsed. Sea caves develop chiefly through wave erosion, a process that continues wherever waves dissipate energy along a coast but proceeds fastest where the host rock is cracked or fissured. Waves can exert enormous force in a confined space through hydraulic action, the scouring of waterborne rock particles, and the pressure of compressed air.

Most large sea caves on America’s West Coast form in basalt, an igneous rock far stronger than sedimentary rock; this lets basaltic caves penetrate deep into cliffs while the surrounding rock face erodes only slowly. The cave at Little River, however, formed in sedimentary rock. Erosion eventually hollowed out a chamber too large for its roof to bear, and the roof collapsed, creating the sinkhole seen today.

The nearby community of Little River was first settled between 1852 and 1856 and was originally known as Beall’s Harbor. A lumber mill built there spurred the growth of a coastal mill town, which in time acquired a schoolhouse, a post office, a shipyard, hotels, stores, and blacksmith shops. Like many other towns on the Mendocino Coast, Little River prospered until the inland timberlands were exhausted; its mill closed in 1893. Since then the town has served mainly as a tourist destination, prized for its beaches and for nearby Van Damme State Park. Read more here and here. Explore more of Little River and the Mendocino Coast here: