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A Geologic Time Line

From Lush Tropics to Arid Desert

Instead of canyons and mountains, a flat coastline and lush tropical vegetation existed at the time this dinosaur roamed the area. Most all of the plant fossils identified from this period are tropical to subtropical species that inhabit wet forests. Animal fossils, including clams, snails, amphibians, reptiles, crocodiles, and small mammals, also indicate a wet lush environment with rivers and thick forests.

Illustration of Parasaurolophus in the dense Kaiparowits forests, by Carel Brest van Kempen from Dinosaurs of Utah by Frank DeCourten, courtesy of the University of Utah Press.

Into this vast low area, tons of mud, silt, and sand were deposited, layer upon layer, over millions of years, recording like pages in a book, events as they unfolded near the end of the age of dinosaurs. These layers of sediment turned to solid rock over time, and are called sedimentary rock. It is in these rocks that ancient plants and animals, or their impressions, are buried and preserved for millions of years. Nearly all of the rock in Grand Staircase-Escalante National Monument is sedimentary, was formed during the age of dinosaurs, and thus could contain important fossil records.

Even though the hadrosaur is millions of years old, it was discovered at the surface of the ground. How could that happen?

Millions of years ago, shifting in the Earth's plates caused a large area of sedimentary rock in the western United States to be lifted up to nearly 1.6 kilometers (1 mile) above sea level. Because it was raised to such high elevation, the erosive forces of wind and water were particularly strong. The area has been carved by erosion as loose rock fell away while resistant rocks – such as sandstone, limestone and lava flows – remained, leaving a vast array of unique features in the landscape.

This uplifting of the land and heavy erosion explains why fossils are often found exposed on the surface in this part of the country. They once were buried under thousands of feet of sediment. Seas covered the land and then retreated. The bones remained. The Earth's crust shifted and the Kaiparowits Plateau was formed. With that swelling came erosion. The thousands of feet of sediment slowly departed leaving the hadrosaur exposed.

To find out more about the uplifting of the Colorado Plateau and some of the many changes in the landscape that have taken place over millions of years, check out the article "High, Wide, and Windswept," one of BLM's teacher resources from Science & Children magazine: http://www.blm.gov/education/colplateau/index.html.

Last updated: 10-23-2009