A six-hour drive from Tucson brought us to Las Vegas. We joined our friends, retired geologist John Zager (Unocal Corp./Chevron) and his wife Sue, who took us on a geo-adventure. Now, I’d like to share the journey with you!
As the saying goes, Las Vegas: Words will fail you. But for geos, this is caused by the rocks, not the slots. Let’s take a look!
Sharon Lyon
Editor, GeoLifestyle
Red Rock Canyon National Conservation Area, Nevada
Aztec Sandstone at Red Rock Canyon; The Keystone Thrust Fault (I have one hand on each side), accessed after a teeth-rattling Jeep ride over a rocky trail.
Red Rock Canyon is a 197,000-acre conservation area located 17 miles west of Las Vegas. It is known for its sandstone cliffs.
Geologic history of Red Rock Canyon:
Throughout the Paleozoic Era, Red Rock Canyon was underwater and limestone was deposited, containing the remains of ancient sea life.
The Paleozoic formations range in age from Cambrian to Permian.
Trip tip: You can view the Permian Kaibab Limestone outcrops along the Fossil Canyon-Fossil Ridge Loop, a 4.4-mile hike. You do not have to hike the entire loop to see fossils. The fossils at Fossil Ridge include sponges, corals, brachiopods, crinoids, and bryozoans that thrived on the ocean floor 250 million years ago.
The seabed slowly rose during the Triassic, becoming shallower. Shale, sandstone, and gypsum were deposited at the time.
By the Jurassic, the land emerged from the sea. Sand dunes spread across the area forming an expansive desert reaching into present-day Utah and Colorado. This sand lithified into the Aztec Sandstone (called Navajo in Utah and Colorado), preserving its characteristic aeolian crossbedding. Iron oxide stained the rocks red.
The sandstones were slowly uplifted thousands of feet, and millions of years of erosion have left us with the spectacular cliffs at Red Rock Canyon.
Compressional forces during the Laramide Orogeny, roughly 66 million years ago, caused the formation of the Keystone Thrust Fault.
Gray Paleozoic limestones were thrust over the red Jurassic sandstones, forming a protective cap.
Trip tip: John said, “To see the thrust fault, you have to go on the jeep trail that snakes to the west behind the Aztec Sandstone bluffs. It is fairly hard to get a great view of the actual fault contact without knowing where you are going. There is a trail called the Keystone Thrust Trail that can be accessed from the Scenic Loop, which will take you to the fault, but it is hard for an untrained eye to pick it out—the fault contact is largely covered.”
Dinosaurs in Red Rock Canyon?
Paleontologists have confirmed fossilized tracks of bipedal dinosaurs in the Aztec Sandstone in three different places. Identified as the ichnogenus Grallator, these small (three-toed) theropods roamed the area 180–190 million years ago.
The park’s resident turtle: Sightings of the desert tortoise are rare within Red Rock Canyon, except for Mojave Max. From April to October, you can visit his outdoor pen at the Visitor Center. The rest of the year he spends in brumation, a type of hibernation. Max hosts his annual emergence contest, visits area schools, and has his own website!
Plan your visit: Begin at the visitor center, with exhibits based around the four elements—earth, wind, water, and fire. Then, drive the 13-mile Scenic Loop Road. The area can experience extreme heat in the summer, so pack plenty of water and sun protection and go early if you intend to hike.
A message from AAPG and MicroSeismic
In continued celebration of International Day of Women and Girls in Science on February 11 and the upcoming International Women's Day on March 8, AAPG and MicroSeismic are showcasing interviews from women leaders in geoscience. This week's featured leader is Michelle Dosey, senior staff geologist at Occidental U.S. Offshore. Here is a sneak peek from her interview:
“A compelling aspect of my job involves utilizing advanced technologies, such as Ocean Bottom Node seismic surveys, to enhance our ability to map and assess our reservoirs. By analyzing these datasets, I can develop more precise geological models, which facilitate understanding resource ranges, optimizing well placement, and planning for secondary recovery techniques.”
Elephant Rock at Valley of Fire State Park; Hiking through the slot canyon.
Known for its 40,000 acres of red, yellow, and purple sandstone, the drive through Valley of Fire State Park is one of the most scenic sites in southern Nevada.
Historic notes:
Early man lived in the area as far back as 11,000 years ago. Petroglyphs carved into the rocks date back to 2,500 years ago and can be seen along Mouse’s Tank Trail and Atlatl Rock. Indigenous Paiutes lived in the valley when the Mormons arrived in 1865.
In 1912, a road was built through Valley of Fire, allowing travel between Salt Lake City and Los Angeles. The valley’s name was coined in the 1920s by AAA.
In 1934, Valley of Fire was opened as Nevada’s first state park.
How to visit: Start at the Visitor Center, which provides exhibits on the geology, ecology, prehistory, and history of the region. Designated areas for rock climbing and repelling, picnicking, and hiking trails are also mapped out here.
Geologic must-sees:
The Aztec sandstone has been sculpted by water and wind to form arches, spires, and domes. These landforms can be seen at such outcrops as the Elephant Rock, Pretzel Arch, and the Fire Wave.
Beyond the sandstones, you can see the gray limestone mountains consisting of Paleozoic rocks that were thrust over the younger Aztec Sandstones.
You can maneuver down a boulder slope to the canyon floor and hike through a slot canyon! The opening began as a crack in the rock, eroding over millions of years from flash flooding to create the natural passage.
The rocks beneath me in the photo are 1.7 billion-year-old Precambrian granites and schists. They were formed in the core of an ancient mountain range. The overlying rocks were eroded away, exposing the core rocks at the earth’s surface.
An unconformity is a buried erosional surface, representing a missing interval of the geologic record. East of Las Vegas, at Frenchman Mountain, you can view the Great Unconformity, which represents about 1.2 billion years of missing time.
The Great Unconformity between the Precambrian and the Cambrian represents 1.2 billion years of missing time.
About 500 million years ago, sea levels rose, and the Precambrian rocks were buried by sand on the sea floor. The sand lithified to become the Cambrian Tapeats Sandstone, seen above the blue line in the above photo. The contact between them is the Great Unconformity.
The Great Unconformity can be seen at the bottom of the Grand Canyon, where the overlying sedimentary rocks are horizontal. At Frenchman Mountain, the rocks dip about 50 degrees east. During the Miocene epoch 6–10 million years ago, Frenchman Mountain slid fifty miles westward along a detachment fault, causing the rocks to tilt.
Read more about Frenchman Mountain and the Great Unconformity here.
Many thanks to John and Sue Zager for being our Las Vegas geology tour guides!
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