Devils Postpile was created when basalt lava erupted and filled a valley along the San Joaquin River. Surface cracks form in the basalt lava as the lava cools and shrinks. Under ideal conditions, surface cracks deepen and form long post-like columns. Devils Postpile is one of the world/s best example of this.

More recent glaciers helped expose a wall of basalt columns. Over time, some of the columns have fallen, leaving a pile of oddly shaped rock as rubble at the base of the wall of columns.

Devils Postpile National Monument is ... (more)