I visited the devils tower when I was a kid and now finding out it is an igneous rock formation. The magma rose through the crust around 56 to 66 million years ago and the sedimentary rock slowly eroded away through millions of years. As it eroded the igneous rock stayed behind leaving the devils tower. Since it cooled slowly it formed larger crystals in the rock. The more the surrounding area erodes it will look taller but that is a long process.