The Devil's Postpile National Monument

The Devil's Postpile

It's one of California's most unique landmarks: the towering columns of columnar basalt looming high over the valley floor is a postcard image for California and the National Park system. Devil's Postpile is a national monument in the Eastern Sierra Nevada Mountains and is a hotspot for tourism between May and November. But enough introduction now, and on to the really interesting part: the geology!

More Columns

The post pile was so named because of its appearance of letters or packages in a large pile, resulting from the erosion and collapse of these tall columns of ancient basalt. Interestingly, this rock is stunningly different from the surrounding rock, which is all white granite formed deep underground and eventually uplifted and carved into the dramatic mountains we have today. Basalt and granite are completely opposite igneous rock types, both in composition and formation. This basalt was erupted from a volcano in a liquid form and left on the surface to cool slowly enough to create these jointed columns of dark rock. When this was erupted from its vent several miles to the north, it flowed down the valley and was impounded probably behind an old glacial moraine and formed a lava lake some 400 feet deep. These columns, usually six sided, resulted from the slow cooling of this lake over hundreds of years.

Looking across this scenic valley to the granite precipice.

All this happened 80-100,000 years before the present, and since then various periods of glaciation have carved the bulk of this lava lake away; smoothing the surface and carting most of the rock away to leave a beautiful meadow-laden valley in its place. After the glaciers melted, the Middle Fork of the San Joaquin River began to flow through the valley and erode the base of the basalt, leaving the columns exposed to ice and gravity, causing much of the rock to become a loose pile of rubble. The result is a 60-foot tall exposure of some of the finest columnar basalt in the world.

Check out the Monument's Website!

Glacial-carved striations and smoothing

Linear scars from rocks in the ice dragged across the surface

Beware of edges

A furry woodland creature crossing the columns.

Columns here are non-veritical and point outwards.

Blocks of basalt are around 900 pounds each and range from 3-7 feet long
on average

Straight down

They are bigger than they look!

The Middle Fork of the San Joaquin River comes right to the base of
another exposure of basalt.

Nearby Soda Springs along the bank of the river.

The peaceful meadow above the Postpile. Soda Springs center left.