Welcome to nature"s bowling alley. Bowling Ball Beach on the Mendocino Coast in California is named after the striking rock formations strewn across the shore. These sandstone balls—a phenomenon known as concretions—formed over millions of years as sedimentary layers built up around a central core of sand and stone held together by mineral cements. Erosion gradually wore away the outer layers to expose the spherical shapes we see today. This created a fascinating spectacle that only appears at low tide. Concretions are rare, and there has been plenty of wild speculation about where they come from, with some believing them to be extraterrestrial debris while others wondering if they are dinosaur fossils. The answer, however, is quite simple: it is the forces of nature at play.