Rainbow Falls at Devils' Postpile National Monument. Devil's Postpile National Monument was established in 1911 by presidential proclamation. It 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. Route 395: Eastern Sierra Nevada Mountains of California.