Until recently, it was thought to have been formed about one million years ago. NPS photo. Because of these traits, basaltic lava tends to have a lower viscosity and will flow more quickly than other lava types. This super-continent was the land mass from which all of today’s continents were born.About 200 million years ago, Pangaea began to split and North America began moving to the West while Europe and Asia moved to the East.
These pieces of accreted land are called exotic terranes and the addition of each terrane to North America took millions of years. Shallow parts of the lava flow would have solidified first, with deeper parts of the lava lake requiring much more time to release the massive amount of stored thermal energy. Some 100,000 years ago, basalt lava flowed from a volcanic vent in the valley of the Middle Fork of the San Joaquin River, filling the valley near the postpile to …
In some cases, the magma rose upwards into the continental crust forming large underground magma chambers. The natural landmark is typically open from mid-June through mid-October (weather permitting) and attracts view-seekers, hikers, fisherman and wildlife-watchers. Current studies suggest that the Postpile was formed less than 100,000 years ago when a cooling lava flow cracked into multi-sided columns. A north-south subduction zone was born, and for millions of years oceanic crust continued to slam into the westward moving North American continent. Encompassing the Devils Postpile formation, Rainbow Falls and acres of stunning mountain scenery, Devils Postpile National Monument is a Mammoth Lakes must-see. The columns of the Devils Postpile formation . Columnar jointing occurs when certain types of lava contract while cooling. Warm shallow seas lapped at the base of the mountains. At this time, the Sierra Nevada would have looked more like the present-day Cascade Mountains of Oregon and Washington or the Andes Mountains of South America. Hornfels near the Minaret Summit and San Joaquin Ridge are likely from this time period as well. Many millions of years would pass before the Sierra Nevada would rise to its current elevations.Beginning about 65 million years ago, the ancestral Sierra Nevada began a long period of erosion. Still, the Sierra was low enough to allow many rivers beginning in present-day Nevada flowed through the mountains en route to the Pacific. Eventually, a glacier later came over this hidden rock formation, polishing the top of the Postpile and exposing one side of it. The lava began filling the valley behind this dam, creating a lava lake 400 ft. deep in some areas. Intermittently, North America would get a big chunk of land added to its western margin as volcanic islands, similar to those of Hawaii or Indonesia, were scraped onto the coast, a process called accretion. It is believed that the headwaters of the San Joaquin began further to the east in present-day Nevada. While all the rifting and moving of Pangaea and North America was taking place, sediments and gravel were steadily eroding from western North American (near present-day Utah and Nevada) and washing out into the shallow sea that covered present-day California. Both of these examples have been highly metamorphosed during the millions of years since their original creation. In this fashion the western edge of North America expanded further and further to the west, and the land we know to be California arrived, piece by piece, like waves from the sea.About 140 million years ago, the friction and pressure between the two plates was so great that the land began to crumple and mountains began to rise east of the subduction zone, the ancestral Sierra Nevada was born. But no force has left a greater footprint on the Postpile than that of glaciers. As the lava lake cooled and solidified from a molten soup to solid rock it began to contract. Powerful erosive forces have been at work during the last 80,000 to 100,000 years carving, shaping and demolishing remnants of the lava flow. The lava that n… Most of the crust slid beneath North America, but occasionally a slice of this sedimentary crust would be thrust onto the continent’s edge.
Basalt columns are a common volcanic feature, and they occur on many scales (faster cooling produces smaller columns). But not all of the magma cooled underground.
It is within this dramatic context that the Devils Postpile formation came to be.An estimated 80,000 to 100,000 years ago a lava vent began spewing hot basaltic lava into the Reds Meadow Valley near present-day Upper Soda Springs, a few miles north of the Monument. The San Joaquin River was one of these. Earthquakes knock columns down into the talus slope below. Some breached the surface creating volcanoes and fissures, spewing lava of varying types onto land. Such depth is uncommon among lava flows and plays a crucial role in the formation of the long columns we see today.
The name "Devils Postpile" refers to a dark cliff of columnar basalt. Radiometric dating indicates the formation was created by a lava flow at some time less than 100,000 years ago.
The park's main feature, the columnar basalt columns, were formed from a plug of cooling lava nearly 100,000 years ago. As North America drifted westward the adjacent oceanic crust was thrust downward and beneath the moving continent. These rocks can be seen from the bridge near Devils Postpile, a ¼ mile walk from the Ranger Station.By about 2 million years ago, the Sierra Nevada began rising quite rapidly. Vestiges of this flow are seen in the dark layered, reddish rocks along the San Joaquin Ridge and above the road near Agnew Meadows. The formation is a rare sight in the geologic world and ranks as one of the world's finest examples of columnar basalt.
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