Pinnacles National park gets its name from rock spires and crags that are remnants of an ancient volcano. The volcano eroded over millions of years as it moved northward along the San Andreas Fault. Rock debris in the form of boulders has weathered and settled, leaving behind spires of volcanic rock and talus caves.
Maine ocean islands provide the only nesting sites for Atlantic puffins in the United States. Eastern Egg Rock in the midcoast region, Seal Island and Matinicus Rock at the mouth of Penobscot Bay, and Machias Seal Island and Petit Manan Island off the downeast coast provide habitat for more than 4,000 puffins each summer.