A Monument to Time

A Monument to Time. . The rocks that house Mesa Verde's cliff dwellings have their own stories to tell. , , Deposition , During the late Cretasceous period (about 90 million years ago) much of North America, including southwest Colorado and the present Rocky Mountains, was covered by a shallow inland sea. , , Thousands of feet of marine and shoreline sediments were deposited and now form the rocks of Mesa Verde: shale, sandstone, coal, and siltstone. , , Uplift and Erosion , Within the last 65 million years, the Colorado Plateau and Rocky Mountains were formed by a series of uplifts that gradually raised the land thousand of feet above sea level. Erosion probably kept pace with the uplift as streams flowed south and west from the rising La Plata and San Juan Mountains. These ancient streams cut deep canyons across gentle slopes of Mesa Verde dissecting it into the smaller, fingerlike mesas on the southern end of the park. , , Over millions of years the Mesa Verde formations were raised almost 8,000 feet and gently tilted to the south. These same sedimentary rocks eroded off the uplifted mountains, leaving a 1,500 foot escarpment between Mesa Verde and the La Plata Mountains. , , (Left Drawing Caption) , Erosion causes natural indentations which were enlarged by Ancestral Puebloans and used as hand-and-toe-hold trails. , , Illustration by Krista Harris, Interpretive Design