The Devils Postpile is a fine example of columnar basalt. Until recently, it was thought to have been formed about one million years ago. Current studies suggest that the Devils Postpile was formed less than 100,000 years ago when a cooling lava flow cracked into multisided columns. Other well-known examples of columnar-jointed lava are the Giant's Causeway in Ireland and Fingal's Cave in Scotland. The Palisades of New Jersey along the Hudson River and the columns at San Miguel Regla, Mexico, are noteworthy, but are less well known. Other occurrences are found throughout the world, but well-developed columns are not abundant.
Some details of the geologic origin of the Devils Postpile are not completely clear, but enough is known to reconstruct much of the story. To understand the geologic setting of the Postpile, we must go back hundreds of millions of years; to a time when sands and muds were being deposited in a vast sea that covered southeastern California and parts of adjoining states.