Devils Postpile National Monument. The monument features the Devils Postpile formation. A very rare geologic site it is one of the world's finest examples of columnar basalt. It's columns tower 60 feet high and display an unusual symmetry. A 2 mile hike from the Postpile takes you to Rainbow Falls. This waterfall drops an impressive 101 feet. About a half mile downstream you can visit the lower falls where the San Joaquin River plunges into a beautiful sparkling pool.