Today, this 1,267-foot-high pinnacle of phonolite (a silica-poor fine-grained igneous rock) is described in many textbooks as an intrusion of igneous rock that never reached the surface to form a ...

A geological cross-section of Devil’s Tower. This is basically what the monument is: an igneous intrusion that was left standing tall by erosion.© ZME Science ...

That could supply centuries of water under current pumping rates. At the same time, the U.S. Geological Survey is finalizing a new estimate of salt water intrusion into parts of the aquifer.

In May, the commission received the latest intrusion assessments from LSU and the U.S. Geological Survey, which conclude that over the past two decades, salt has spread into various layers of the ...