"Geologists Carpenter and Russell studied Devils Tower in the late 19th century and came to the conclusion that it was formed by an igneous intrusion. Modern geologists agree that it was formed by the intrusion of igneous material, but not on exactly how that process took place. Several believe the molten rock comprising the Tower might not have surfaced; others are convinced the tower is all that remains of what once was a large explosive volcano.
In 1907, scientists Darton and O'Harra decided that Devils Tower must be an eroded remnant of a laccolith. A laccolith is a large mass of igneous rock which is intruded through sedimentary rock beds without reaching the surface, but makes a rounded bulge in the sedimentary layers above. This theory was quite popular in the early 20th century since numerous studies had earlier been done on laccoliths in the Southwest.
Other theories have suggested that Devils Tower is a volcanic plug or that it is the neck of an extinct volcano. Presumably, if Devils Tower was a volcanic plug, any volcanics created by it volcanic ash, lava flows, volcanic debris would have been eroded away long ago. Some pyroclastic material of the same age as Devils Tower has been identified elsewhere in Wyoming."
Devils Tower - Wikipedia, the free encyclopedia
Another example of this peculiarly columnar phenomenon is a flow on slope of the Sierra Nevada, called The Devil's Postpile National Monument. It is however a flow of basalt rather than the phonolite porphyry of the Devil's Tower.
Now I learned all this over 50 years ago in a summer-school course I took between the 9th and 10th grades, and I know the information is out there for anyone to find fairly easily on Wikipedia or at the site of the National Park Service, so I also know if you really wanted to know the answer to your question you could have looked it up.
I thus conclude that either:
1. You were too stupid to know that you could look it up. I regard that degree of stupidity unlikely, but, at least, it would not be your fault.
2. You were too lazy to look it up. This is, I would suppose, a possibility, but does reveal a distinct character flaw.
3. You don't really care about the answer, but thought you could confound someone in argument. This would be fairly dishonest.
Is there some other reason you asked the question, and avoid acknowledging the answer? Inquiring minds want to know.