Stop 3: Zion National Park
The canyons we see is the Navajo Fm above the Moenave Fm. The tallest parts are Navajo with a little bit of the Carmel Fm on top and are 2000 feet high. This formation is all over Utah and up to Montana. The sand that makes up this sandstone was fine grained wind deposited, or eolian, dune sand. There is lots of large-scale tangential crossbedding. The wind during this lower Jurassic time was mostly from the north and northwest. The sand piled up to 2000 feet thick over 20 to 25 million years. We are looking at a cross-section of a giant ancient dune field, called an erg. This is like the Sahara is today. This sand buried the terrain where the dinosaurs lived in earlier wetter times. As the climate became drier, the dinosaur's food supply dwindled. However, there were some oases where dinosaur footprints have been found. The dinosaurs who stayed here adapted. If we trace the sands to the north we find the Sundance Fm, a beach sand deposit.
This is also part of what is called the Grand Staircase. These are slightly tilted layers of hard and soft strata. The hard layers erode into cliffs and the soft layers into slopes. We entered the level of the Wingate (Moenave) sandstone or the Vermillion Cliffs.
We take Highway 89, then Highway 12 toward Bryce Canyon.
Stop 4: Dixie National Forest
This is the entrance to Bryce Canyon National Park. We stop at Red Canyon, called the Pink Cliffs, the final rung of the Grand Staircase. This is the western margin of the Colorado Plateau. We see in the rocks across the road the Sevier Fault. On the left, downdropped side are volcanic basalts of a few thousand years ago. On the right, or upside is the Claron Fm 40 million years old. Only when we get to the other side of these Eocene rocks and pass the Paunsaugunt Fault will we be back in Cretaceous rocks. (Our instructor, Frank DeCourten, is the author of the geology book on Bryce Canyon - Shadows of Time.
We leave Bryce and turn right on Highway 12, go down through the Claron Fm and cross the Paunsaugunt Fault. We cross the dry Paria River which flows into the Grand Canyon.