The Glass Beach is not made by nature but bears the testimony of sea waves covering up for mistakes made by men. Residents of Fort Bragg used to throw their garbage over the cliff, into the ocean during the early part of the 20th century. By 1949 the area became a public dumping place for all sorts of unusable including cars containing lot of glass. This was banned in 1967 and during several decades afterwards, sea waves cleared the beach leaving glass pieces behind forming the Glass Beach. Scroll down the page to see at the photos of the place.
Sources: Wikipedia, Fortbragg.com (h/t: boredpanda)