Several mountain ranges have been uplifted and subsequently eroded away before the rise of the Rocky Mountains you see today. The geologic history of Colorado started nearly two billion years ago, and is recorded in the old rocks seen in the mountains to the west. We start our discussion 72 million years ago, when Colorado was inundated by an inland sea.

An ancient shallow seaway covered much of Colorado and deposited marine shale (mud and clay) forming the Pierre Formation.

The inland sea retreated with the beginning uplift of the Laramide Rocky Mountains. Rivers carried sediment from the mountains to the shore (Fox Hills Formation). Along the rivers, sand, clay, and coal were deposited in alternating layers. These river and swamp deposits are the Laramie Formation. Dinosaurs and plant debris made impressions on muddy surfaces before being buried by sand that washed in from periodic floods. The rocks where you are now standing are about 68 million years old. The following diagrams show how the rocks you see along the Triceratops Trail were formed.

When dinosaurs left their tracks at this site, the environment was similar to the swampy Mississippi Delta region of modern-day Louisiana.

River channels were flanked by swamps where clay and coal deposits formed.

During periodic floods, the river breached its banks, spilling sand across the swamps. This repeated flooding created the alternating sand and clay layers that we see here.

Sign sponsored by SCFD, the Colorado Scientific Society, and Dr. Robert Weimer.