Some things take a long time

Established in 1911 by presidential proclamation, Devils Postpile National Monument protects and preserves the Devils Postpile formation, the 101-foot high Rainbow Falls, and the pristine mountain scenery in California's High Sierras. The formation is a rare sight in the geologic world and ranks as one of the world’s finest examples of columnar basalt. Its columns tower 60 feet high and display an unusual symmetry.

Approximately 100,000 years ago, a lava flow erupted two miles upstream from the location of today's Monument. As it flowed down the Valley, it eventually ran into an obstruction which served as a dam to the lava's path. Pooling up to as deep as 400 feet behind the natural dam, the lava cooled. Conditions were such that the lava--that was incredibly uniform in its mineral composition--cooled at a very slow rate. As it cooled, it contracted and cracked, forming hexagonal columns. 80,000 years later, a glacier flowed through the same valley, overriding the formation and eventually revealing the sides and tops of the columns. Glacial polish can still be seen today at the top of the formation.
Rainbow Falls