Devil's Postpile National Monument
The Devil's Postpile, an unusual formation of many
tall columns of basalt, presents a textbook example
of the volcanism that helped to form the Mammoth Lakes
region of the Sierra Nevada mountain range.
The molten basalt flowed southward and poured into
the Middle Fork of the San Joaquin River valley, filling
it to a depth of more than 400 feet. As the lava cooled
and solidified, it shrank, creating cracks radiating
from the center, approximately two feet apart. Eventually,
the cracks joined, also growing downward. A large glacier
quarried away most of the columns, leaving remnants
on both sides of the valley, of which Devil's Postpile
is the largest. The tremendously heavy mass of ice created
a highly polished basalt, some of which is still visible,
though much of it has weathered away during the thousands
of years since.
Today frost-wedging and ice continue to cause the giant
posts to fracture and fall.
The Devil's Postpile is an important site for visitors
to experience. It offers some insight into the fascinating
geologic history that created this awesome area. Information
regarding tours and hikes is available at the Mammoth
Lakes Visitors' Center, located on Highway 203.