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 located just off U.S. Highway 395, near Mammoth Lakes, California, just southeast of Yosemite National Park.

Mark Wasson, http://www.markwasson.com > Trips has detailed summaries of my trips