Devil's Postpile National Monument was proclaimed to protect a rare geological formation called Devil's Postpile and also nearby Rainbow waterfalls. Devil's Postpile is a cliff of basalt rock and is a fine example of columnar basalt. The symmetrical and multi-faced basalt columns are about 60ft high. Recent study shows the formation is about 100,000 years old and was was formed by a cooling lava flow. The columns might have been much taller. The eroding forces have broken the columns and the pieces can been in heaps on the ground.
