Between the dates of May 2nd through 10th of 1998, a group of geology students from the University of Tennessee at Chattanooga participated in an in-depth, on location study of certain sites in Nevada, California, Arizona, and Utah. In this report, the locations studied will be given in chronological order. It should also be noted that for an entire semester before this trip the participants of it were enrolled in a class in which to study the locations visited.
May 2nd was the day we landed in Las Vegas; we arrived quite late and traveled immediately to a campsite near Lake Mead. This site was north of Las Vegas and only about two miles east of The Valley of Fire State Park. May 3rd was the first true day for our geological exploration. We left from our camp and drove toward The Valley of Fire. As we drove we approached an area on the right side of the road with small sandy hills capped by basalt. It was hypothesized that the soft sand was probably Mesozoic in age, and the basalts were Tertiary in origin. The hills were present because the basalts were harder that the soft sands and did not erode as quickly causing these hills.
Next we drove onward to The Valley of Fire State Park. This site is famous for being in numerous films and TV shows like Star Trek: Generations and Bill and Ted's Bogus Journey just for example. Unlike most of the area we will be discussing, this location is dipping to the east. The bright orange sandstone is of the Navajo Formation. The cause of this eastward dipping section of sandstone is probably the result of the Lake Mead left lateral strike slip fault.
As we drove to the south into Las Vegas, we encountered the Keystone Thrust just west of the city at La Madre Mountain. Here we observed both the Keystone and the Red Spring thrusts. It was seen that the Keystone thrust lay above Paleozoic strata and this lay above the Red Spring thrust. All of this was above the Aztec Sandstone (another name for the Navajo Sandstone).
Next stop was a Tertiary landslide at the Calico Basin. "This mass is mainly brecciated Mississipian-Devonian rocks, and was originally mapped as part of the thrust plate by Longwell [1926] but was interpreted as a Mesozoic landslide deposit by Davis [1973] and as a Tertiary landslide deposit by Axen [1984] because it overlaps one of the high-angle faults which cut both the Keystone and Red Spring thrusts" (IGC 17-18).
As we drove on that day, we reached a point 3.7 miles east of Shoshone, California on State Highway 178 moving west. On the right side of the road there is a spectacular roadcut. "The rocks consist of Tertiary sedimentary and volcanic rocks deposited upon tilted Cambrian rocks of the Bonanza King Formation" (Troxel and Heydari 91). The rocks in the roadcut all tilt to the west. The rocks mentioned are overlaid by rhyolitic ash flow tuff. A layer of dense dark vitrophyre notably marks this. All tuff layers were caused by deposition of ashflow and air-fall tuff units.
Next we visited the Amargosa Chaos. Chaos material usually includes both Tertiary and Cambrian material. This location includes, "Precambrian sedimentary rocks and diabase, Cambrian sedimentary rocks, and Tertiary volcanic, plutonic, and sedimentary rocks; and an autochthonous cover of Late Cenozoic fanglomerate, basalt, and alluvium" (Troxel and Wright 121).
On the evening of the 3rd we camped in the Panamint Range just west of Death Valley. We camped at a mine entrance.
On the 4th of May we traveled through Death Valley, California. We focused our study on the turtlebacks in the region. There are three turtlebacks in Death Valley. From south to north these are Mormon Point, Copper Canyon, and the Badwater turtlebacks. Turtlebacks are actually megamullions that push deep underneath Death Valley. All three push forward from the Black Mountains. They were actually formed before the pull apart basin began to form the valley exposing the turtlebacks.
Death Valley itself is the lowest point in the United States at a depth of 282 feet below sea level. The low humidity and high temperature causes very little water to exist here. Flat salt plains spread for miles everywhere between the Black Mountains and the Panamint Range. Excellent pictures were taken of these salt plains. North of the Turtlebacks there are sand dunes that are present. These dunes were used during the filming of Star Wars.
We then drove onto the Black Mountains to a location called Dante's View. This point offered and excellent view of Badwater. We were directly above the turtleback at an elevation of 5,475 feet.
That evening we returned to Las Vegas, Nevada and stayed the night at the Frontier Hotel.
The next day on the 5th we drove into Arizona across Hoover Dam. Most of this day consisted of driving. There were several times, however, that we did get to stop and view the Vishnu Schist. The Schist is Precambrian in age and will later be seen at the base of the Grand Canyon.
That evening we camped near Joseph City. From our campsite we could see across Interstate 40 to an excellent outcrop of epsilon cross-stratification.
On May 6th we drove to Petrified Forest National Park. Here there are many examples of petrified wood. This area at one time was an Upper Triassic forest. Everywhere you look here there will be an example of these trees. There are also examples of early dinosaurs here. Some examples are Placerias, Desmatosuchus, and a dinosaur nicknamed Gertie. Next we drove across I-40 once again and viewed the north section of the park, which includes the Painted Desert, and mounds of Tertiary Basalts.
The next stop was Meteor Crater, Arizona. "Meteor Crater was the first recognized impact crater on Earth; it remains the largest known crater with associated meteorites" (Shoemaker 399). Here about 49,000 ± 3,000 years ago a large meteorite smashed into the Earth at a speed of 12 miles per second. The resulting explosion had the approximate power of 15 megatons of TNT.
Our next stop was next to Sunset Crater momentarily to examine the most recent cinder cone volcano in the area. Not to far from Flagstaff, Arizona, Sunset Crater was active between 1064 to 1184 AD It is associated with the San Francisco Volcanic Field. Excellent examples of scoria litters the ground near Sunset Crater.
SP Mountain was our next stop. Like Sunset Crater, SP Mountain is a cinder cone volcano. The difference is SP Mountain was active approximately 71,000 years ago. Flowing north from the volcano is an excellent example of a block lava flow. A table of the chemical analysis's of both SP Mountain and SP Flow was given by Ulrich working from other data he researched. A CIPW chart and TAS diagram is included in this booklet in the Charts & Graphs Section.
At the end of the day we had reached The Grand Canyon.
At this point, it would be good to understand the different formations, which are present at The Grand Canyon. Knowing these also assists us in understanding the stratigraphy of other areas in the region. At the base of the canyon where the Colorado River flows exists the Vishnu Schist which is Precambrian in age. Above that, in order going up, is the Tapeats Sandstone, Bright Angel Shale, and the Muav Formation; these are Cambrian in age. Next up is the Devonian aged Temple Butte Limestone followed by the Mississippian Redwall Limestone. Further up is the Pennsylvanian Supai Formation or Group (consisting of the Watahomigi Formation, the Manakacha Formation, the Wescogame Formation, and the Esplanade Sandstone that is actually part of the Permian). In the Permian we have the Hermit Shale, followed by the Coconino Sandstone, the Toroweap Formation, and the Kaibab Formation. In some parts of the Grand Canyon (Especially on the western sections) The Triassic Moenkopi Formation is available, along with some Tertiary lava.
The canyon itself was formed approximately 5.5 to 1 million years ago. It was formed by "regional extension and reactivation of high-angle faults as normal faults" (Ulrich). There have also been numerous lava flows during the past 1.5 million years, which appears along the western river channel.
We stayed this night at The Grand Canyon as well.
On the following day we drove north into Utah to Capital Reef National Park. On the way we drove through many examples of eolian cross-bedding seen in the Navajo Sandstone (Examples of eolian environments are also seen in the Coconino Sandstone). Most of the day was spent driving to Utah. Therefore we camped early at Capital Reef National Park. Although anthropology and geology are two different sciences, a group of us enjoyed an excellent lecture on the Ute Indians who inhabited the area before white settlers arrived.
May 9th was a busy day, which encompassed an extensive visit to Capital Reef. We traveled through the Morrison Formation which is Late Jurassic in age (See Circle Cliffs – Capital Reef National Park diagram in the Charts and Diagram section to what other formations are exposed). Several locations of extreme interest were the Temple of the Sun and Temple of the Moon. Another bizarre attraction was Glass Mountain, which is a large outcrop of gypsum. Capital Reef is well know for the Waterpocket Fold. "The Waterpocket fold formed about sixty million years ago when a subsurface fault shifted, bending the rock layers above. This produced a monocline (a fold with one steep side). Rock layers are tilted as much as sixty degrees from their original horizontal position; 7,000 feet higher on the west side than the layers on the east" (Cliffline 10).
Our next major stop was Bryce Canyon National Park. This location provided us with the youngest rocks on the tour. The ages ranged from the Tertiary Wasatch Formation to the oldest present Navajo Sandstone of Jurassic age. Brilliant spikes protrude into the sky around the area of Bryce Point.
The final stop for the day was Zion National Park. Here we camped for the night. On the 10th we arose for the last time on our trip and began exploring Zion. The giant Mesozoic cliffs allow us to see the massive size of the Navajo Sandstone. Eolian beds are clearly seen along the walls of the sandstone.
At this point we traveled south to St. George, Utah to see the past volcanics of the region. In the basin "is a series of late Cenozoic basaltic flows that were extruded near the base of the Pine Valley Mountains and flowed southward into the ancestral drainage of the Virgin River" (Hamblin 291). Several cinder cone rise out of Diamond Valley. We also picked up some excellent samples of scoria.
After the visit to the St. George Basin, we drove south on Interstate 15 to Las Vegas where we boarded a flight home.
Looking back on the mountain-building history of the southwest there are several episodes worth noting. The Antler Orogeny occurred during the Devonian at approximately the same time as the Acadian in the southeast. The next orogeny occurred at the border of the Permian and Triassic. This orogeny was called the Sonoma. The Nevadan Orogeny occurred at the Jurassic-Cretaceous boundary. The Sevier was in the middle of the Cretaceous. The Laramide Orogeny happened at the same time of the extinction of the dinosaurs along the K-T (Cretaceous-Tertiary) boundary. Finally, the Coast Ranges Orogeny happened in the Cenozoic. This demonstrates how much younger the mountains in the southwest are compared to the Appalachians are in the southeast. The last Orogeny in the southeast was the Alleghanian which ended at the end of the Permian about 300 million years ago. Compare that information with what was previously states about the Coast Ranges Orogeny that occurred in the last 50 million years.
The geology of the southwest is such a wonderful topic of study because of its recent development, it's easy accessibility, and also it's easy ability to be view due to the absence of trees and other obstructions. I hope this has been informative.