Devil's Postpile National Monument

The Devil's Postpile, an unusual formation of many tall columns of basalt, presents a textbook example of the volcanism that helped to form the Mammoth Lakes region of the Sierra Nevada mountain range.

The molten basalt flowed southward and poured into the Middle Fork of the San Joaquin River valley, filling it to a depth of more than 400 feet. As the lava cooled and solidified, it shrank, creating cracks radiating from the center, approximately two feet apart. Eventually, the cracks joined, also growing downward. A large glacier quarried away most of the columns, leaving remnants on both sides of the valley, of which Devil's Postpile is the largest. The tremendously heavy mass of ice created a highly polished basalt, some of which is still visible, though much of it has weathered away during the thousands of years since.

Today frost-wedging and ice continue to cause the giant posts to fracture and fall.

The Devil's Postpile is an important site for visitors to experience. It offers some insight into the fascinating geologic history that created this awesome area. Information regarding tours and hikes is available at the Mammoth Lakes Visitors' Center, located on Highway 203.