Devils Postpile National Monument - http://www.nps.gov/depo

Established in 1911 by presidential proclamation, Devils Postpile National Monument protects and preserves the Devils Postpile formation, the 101-foot high Rainbow Falls, and pristine mountain scenery.
The Devils Postpile 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. Another wonder is in store just downstream from the Postpile at Rainbow Falls, once called “a gem unique and worthy of its name.” When the sun is overhead, a bright rainbow highlights the spectacular falls.

The monument is also a portal to the High Sierra backcountry; some 75% of the monument is included in the Ansel Adams Wilderness.