Field Trip-Geology of Dinosaur Country

An Exploration of the Geology and Paleontology of Utah and Colorado

Geology 16G - Sierra College Summer Semester 1998 - Frank DeCourten

This course is designed to offer students an opportunity to participate in a 10-day field study of the Mesozoic geology, geologic history, and ancient environments of the central Utah and western Colorado region. Over the past 150 years, the Mesozoic rocks of this area have produced thousands of dinosaur fossils, revealing a magnificent menagerie of ancient reptiles that lived in North America. Studies of the fossil-bearing rock units have allowed geologists to reconstruct the habitats and environments in which these dinosaurs that left the fossils, to gain an understanding of the manner in which their remains were preserved, and to observe the evidence for over 160 million years of change in the environment and dinosaur faunas of a spectacular region of North America.

The field trip began July 12, 1998, as we left Sierra College about 8:40 a.m.. Our initial milage in our van was 62,068 miles. We took Interstate 80 up over the Sierra Nevada into Nevada. At Fernley we take Highway 50 through central Nevada. Southeast of Ely we take Highway 93 south. Our first night's camp site was in the Nevada desert south of Ely off Cave Valley Road. The next morning we stopped at Cathedral Gorge State Park. This is the Panaca Fm, remnants of a Plio-Pleistocene (approx.1 million years) lakebed. When the lake drained away it left lakebed sediments which have eroded away forming scenic cliffs and canyons.

The Nevada Great Basin is stretched crust with fault-block mountains. The gray limestone bedrock is Paleozoic with Cenozoic brown orange volcanics on top of some mountains. The valleys are filled with sediments from these mountains. There are few Mesozoic sedimentary rocks in Nevada so there are no dinosaurs to be found here. The mountain ranges near the border with Utah mark the boundary of the Great Basin and the Colorado Plateau(s). The rocks east of the Great Basin are mostly Mesozoic. St. George, Utah, our next stop is on the edge of this province. We take Highway 319 east, then 18 south.

As we approach St George, there are Quaternary cinder cones on the left of the road. These basalts are between 2000 and 20,000 years old. We turn right into Snow Canyon and see the Navajo Fm, the first of many times we'll see it. These are crossbedded sandstones and the different colors are due to oxidation. There is a lava flow capping some of it which flowed all the way into the Grand Canyon.
Outside of St. George we stop at our first site near Washington, UT.

Stop 1: Washington Track Site

Here we look at the earliest evidence of dinosaurs in Utah - footprints in the Moenave Fm. (Strata of this same age deposit are known as the Wingate Fm in eastern Utah.) This is fine sandstone which was stream deposited. Erosion-produced sediments from early Jurassic low mountains to the west were deposited here by streams flowing from the west. These footprints are in limestone, suggesting a body of standing water which was probably what drew the dinosaurs here. There have been few bones of dinosaurs found in the Moenave Fm. These few footprints were exposed when a nearby water reservoir spilled over and washed away the sand deposits in this small gully. This site is unmarked.

We continue on to our next camp site in Warner Canyon.

Stop 2: Warner Canyon Track Site

This is still the Moenave Fm. This tracksite has been developed by the BLM with the tracks explained by a sign. There are big tracks here and small bird-like tracks. The big tracks are from a prosauropod that walked both quadripedally and bipedally. The small tracks are from a bipedal carnivore therapod. Bones of a prosauropod have been found in this same formation. Teeth of a slender ten foot therapod have also been found.

Click image for a larger view.

We take Highway 9 toward Zion National Park and enter the south entrance.

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