Composed of basalt, these rocks were formed by lava flows emanating from the Blue Mountains and Columbia basin about 15-16 million years ago. The lava flows created many of the Oregon coast's natural features. The rocks were once joined to the coastline but years of erosion have since separated the monoliths from the coast. The rocks are home to many intertidal animals, including starfish, sea anemone, crabs, chitons, limpets, and sea slugs. They are also nesting sites for many sea birds, including terns and puffins.