The claim started as satire
The source of the Facebook postings appears to be a July 2017 story from the satirical Casper Planet Facebook page.
Other postings on Casper Planet include peaceful protesters calling on their leaders to classify vehicles as deadly weapons so they can block highways and white males across the country seeking "reparations" for insults to them.
Casper Planet’s post cites
www.infinitysnews.com, which does not exist. The image purportedly showing “the roots” of the tower actually shows the root system of sweet corn at 8 weeks
The geological evidence is clear, Devils Tower is a rock structure and was not a giant tree. But debunking the giant tree theory does not make Devils' Tower any less enthralling. It is a unique and magnificent structure and we encourage everyone to see it and explore it in person.
The National Park Service, which actually has jurisdiction over Devils Tower, flatly states it "is formed of a rare igneous rock, phonolite porphyry" and is a geological marvel, not a botanical one.
"The simplest explanation is that Devils Tower is a stock — a small intrusive body formed by magma which cooled underground and was later exposed by erosion," the NPS said, saying it formed around 50 million years ago.
It is flat on top but round on the bottom.