A. When the sea covered much of Texas 65 to 135 million years ago! In Central Texas, it's possible to walk through a sea and keep your feet dry because much of our state was covered by a shallow sea during the Cretaceous Period, approximately 65 to 135 million years ago. Sediments deposited in this shallow sea were transformed by geologic processes into limestones, dolomites, and marls of the Lower Cretaceous and chalks and clays of the Upper Cretaceous. This was a time when dinosaurs roamed the land, and many of their bones and footprints, as well as the remains of marine animals, were incorporated into Cretaceous rocks.
Over time, other sediments consisting of sands and clays were deposited on top of the limestones and dolomites. Over more time, faults caused the rocks to begin to shift. Erosion began to remove some of the sediments and exposed the Cretaceous rocks. Many natural areas in Central Texas have exposed layers of Glen Rose, Edwards, and Walnut rock formations due to erosion. Close examination of the rocks under our feet will reveal fossils of marine life that existed here long ago, when the shallow seas covered Central Texas.