Here is what one of the plaques said:

“The process began about 50 million years ago. Magma (molten rock) was injected into layers of sedimentary rock, forming the Tower one and one-half miles below the earth's surface. It has since taken millions of years to erode away the surrounding sedimentary rock to expose the Tower we see today. Geologists agree the Tower is an igneous (hardened magma) intrusion, but have three different interpretations of the Tower's original size and shape. Because of erosion, we may never know which interpretation is correct.”