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We loaded the vehicles, guidebooks were distributed, and we hit the road for Zion. Along the way we looked at the deep soil development on the Mormon Plateau, watched for rocks in the Virgin Gorge, and drove across the Hurricane fault. After a long drive we arrived in Zion and set up camp. (Click on photos for additional images.)
In the morning we were treated to awesome views from our campsite. Doug Yule and Dick Heermance gave a presentation on the geologic history and development of this region. They spoke about the physiography, stratigraphy, seismicity, the Grand Staircase, and the nature of the transition zone between the Basin and Range and Colorado Plateau.
We boarded a shuttle bus and headed up Zion Canyon for the Narrows. Along the way we saw some of the highest sandstone cliffs on the planet. At the Narrows we hiked through the river among towering walls of Jurassic Navajo sandstone. Some of the more intrepid adventurers swam through deep pools and continued hiking up the river.
After the Narrows hike we went back to camp, got into the vehicles, and headed for eastern Zion. We got our last look at Zion Canyon and the Great Arch and then headed through the tunnel. Windows in the tunnel provided some great but fleeting views.
At Checkerboard Mesa Dick Heermance illustrated the process of dune cross bed formation and how paleowind direction is determined. He also explained what evidence is used to determine if cross beds are eolian or water generated. Robinson Cecil pointed out that some of the sands in this Jurassic dune field came from as far away as the Appalachian Mountains. And finally Doug Yule posed the question as to what process was responsible for creating the “squares” on the checkerboard.
We left the terrestrial deposits and at our next stop looked at the Tropic Shale (elsewhere known as the Mancos) and Dakota Sandstone in the Cretaceous section. Doug Yule described the components of the Grand Staircase (to the east we could see the White Cliffs) and faults along the western edge of the Colorado Plateau.
Our next stop was Coral Pink Sand Dunes State Park. The dunes consist of eroded Navajo sands that were funneled between two mountain ranges and piled up along the Sevier-Toroweap fault. We spent the remaining afternoon frolicking in the dunes. We cooked hobo pockets in the fire ring coals and then were treated to a special sunset amid threatening skies.
In the morning Doug Yule and Dick Heermance spoke about some of the geologic features that we would see that day. We traveled down the Vermillion Cliffs and onto the Moenkopi formation then onto the Kaibab and Uinkaret plateaus. At the eastern edge of the Uinkaret volcanic field we stopped to examine Pleistocene basalt flows and cinder cones. Then we stopped along the Toroweap fault where Doug Yule talked about the fault separation and age. Next we entered Grand Canyon National Park and drove to Tuweep where we set up camp.
We hiked to the canyon rim where we were treated to spectacular views of the Grand Canyon, Colorado River, Vulcan’s Throne, and Lava Falls, a legendary rapid for river rafters. On several occasions lava flows from the Uinkaret volcanic field have cascaded over the rim and dammed the Colorado River creating huge lakes.
While waiting for a storm to skirt our camp the geology faculty presented some important concepts on the geology of this region. Some of the topics covered included: margin features of the Colorado Plateau (it behaves as a single block despite tectonism on all sides), timing and tectonics of Colorado Plateau uplift determined by thermochronometry (using apatite crystals), early- to mid- Tertiary unroofing, tertiary rim gravels (old river system that had eroded part of the plateau), the Mogollon Rim, and erosion of the Grand Canyon in the last 5 Ma.
After a spectacular sunrise we gathererd around the van for a morning lecture. With geologic maps ablaze Dick Heermance and Doug Yule went over the geologic history of the Grand Canyon including the statigraphy and a discussion of the Great Unconformity. They then described some of the geologic features that we would see on our route home.
We left Tuweep and headed across the Uinkaret volcanic field near the forested summit of Mt. Trumbull and then on to the Hurricane cliffs. From there we had a nice view of the Shivwits Plateau. The surface at this stop was capped by a cobble conglomerate.
On our last leg of the trip we crossed the Hurricane fault and followed the Hurricane cliffs for quite some distance. We bid adieu to the Colorado Plateau as we exited the Virgin Gorge and headed back to CSUN.