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Rockin’ the past: Northeastern Nevada’s geologic mysteries

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Rockin’ the past: Northeastern Nevada’s geologic mysteries

Retired geologist Ronnie Joe Varnell holds a rock with a fossil that was found at Fossil Hill north of Elko.

ELKO – If you ever find yourself between a rock and a hard place, you must be in Nevada. Nevada is just a “rocky” place. In fact, it is difficult to travel almost anywhere in the state and not be surrounded by rocks.

Even though stones and earthen formations are a daily experience, their mystical appearances are awe-inspiring, often leaving the visitor with more questions than answers.

There are fossils just a stone’s throw from Elko, off Mountain City Highway. Large, rounded boulders on the road to Jackpot are a reminder of Yellowstone’s volcanic history. Towering rock formations called hoodoos greet travelers near Jarbidge and Carlin. And Lamoille Canyon is a showcase illustrating the powers of glaciation and tectonics.

Fossil Finds

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Rockin’ the past: Northeastern Nevada’s geologic mysteries

Several types of fossils can be found at Fossil Hill north of Elko.

Fossils are abundant. Everything from ammonites to trilobites can be found if you know where to look. Elko’s own Fossil Hill is located just off of Mountain City Highway. Many of the fossils here are plant remains, according to former geology instructor Michael McFarlane. However, animal fossils can be found as well.

“The most abundant animal fossils at fossil hill are crinoids, brachiopods and bryozoans,” McFarlane said.

Crinoids have been around since the Ordovician Period, about 490 million years ago. They are sometimes called “sea lilies,” but they are animals, not plants. Crinoids are related to starfish and other spiny echinoderms. A common physical characteristic of these animals is a five-point radial symmetry.

Finding a whole crinoid is a rare thing. Usually people uncover short “stems.” When the animals died their soft bodies decomposed and their skeletal remains were swept about by the seas, breaking them apart.

Brachiopods have been around for about 550 million years. Their descendants survive in today’s oceans. Resembling an oyster, the remains of these animals can be found in most parts of the world.

Brachiopods attach their fleshy pedicles to rocks or other hard surfaces. The shells open and close, allowing food to drift inside to be consumed.

Bryozoans live today and they are also among the most prominent creatures in the fossil record. They are also from the Ordovician Period, around 470 million years ago.

These animals live in colonies. Two Greek words were combined to form the name bryozoan, bryon (moss) and zoon (animal.) In their communal lifestyle they often resemble moss.

Big Boulders

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Rockin’ the past: Northeastern Nevada’s geologic mysteries

These rounded boulders near Jackpot were once hot magma.

The rounded boulders west of Jackpot resemble a giant’s marble game in my mind. These lithics are igneous in origin and have weathered over time to produce the hummocky look we see today.

These rocks came about during the time when the Yellowstone hot spot was most active, according to McFarlane.

The rocks are granitic in composition and were once hot magma that intruded overlying formations. Then they cooled and were exposed. An exfoliation process took place, according to retired geologist and gold assayer Ronnie Joe Varnell.

The Yellowstone Hotspot is a hot, upwardly directed plume of the Earth’s mantle. Three massive eruptions happened at Yellowstone about 2.1 million, 1.3 million and 640,000 years ago. This type or eruption produces catastrophic damage. According to earthsky.org, an eruption from this super volcano could blanket all of North America in ash and alter the worldwide temperature, causing it to cool.

Most scientists doubt if another eruption will occur any time soon. However, experts continue to monitor the region. If an eruption is imminent, scientists believe they can predict the event weeks or months in advance.

Geologist John Bernt feels the theory of the Yellowstone hotspot is incorrect. But, he does believe that these boulders are weathered granitic rocks. The copper found in the area is directly related to them, according to Bernt.

“On the north side of the mountain you will see some old mine workings which were explorations for copper and silver,” Bernt said.

Tall Towers

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Rockin’ the past: Northeastern Nevada’s geologic mysteries

The Jarbidge hoodoos are dominant pillars just outside the remote town in northern Elko County.

The tall formations just outside of Jarbidge are large rhyolite and basalt outcroppings. Rhyolite is an igneous formation dating back to the Miocene and Pliocene Epochs, about 23 to 5 million years ago and 5 million to 2.5 million years ago, respectively. People have named some of them because of their pointed nature as in Banana Rock and Castle Rock.

Indigenous people believed in a legendary large creature called Tsawhawbitts who would gather the Shoshone people in a basket and eat them for dinner. According to the myth, these people got tired of being preyed upon and decided to trap the beast in the canyon. They chased him into a cave and sealed it with stones, forever ending his brutality.

Folklore seems to come to life when gazing at these magnificent towers that resemble living sentinels. Who knows, maybe Tsawhabitts transformed himself into rock and still rules the canyon?

A more scientific explanation is that these vertical rocks are remnants of the canyon wall that receded back due to water erosion, according to Varnell.

Bernt said the Jarbidge River Canyon and other tributaries of the Snake River formed after the Snake River Canyon formed.

“The Bonneville flood event caused the cutting of the Snake River Canyon, which allowed incisions like Jarbidge Canyon,” Bernt said.

The timeframe of the Bonneville flood event was about 17,120 years ago, according to sources Bernt has researched. However, he feels this date is a bit too old because a lot of the glacial melting had not occurred yet.

The pinnacles erupted out of the Snake River Plain called the Bruneau-Jarbidge Eruptive Center. The center also goes through Murphy’s Hot Springs in nearby Idaho.

“These are ignimbrites or ash flow tufts,” Bernt said. “An ignimbrite occurs because of a silicic volcanic event and as the magma rises it will start to visiculate. The dissolved gasses start to come out of the melt and form bubbles. Expansion of the bubbles accelerates the flow of the magma, but when they reach the atmosphere and there is much less confining pressure, the bubbles will blow apart and that forms a volcanic ash. The ash was extremely hot and blown in the air into columns that might have been many kilometers high.”

As these columns blew up, gravity pulled them down and the ash particles touched and flowed outward.

“Each of those layers is made up of an unimaginable number of tiny ash particles that were remelted together,” Bernt said.

Melting Mountains

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Rockin’ the past: Northeastern Nevada’s geologic mysteries

The Glacier Overlook pullout in Lamoille Canyon yields a spectacular view and tells the story of an icy past.

Glacier Overlook in the Ruby Mountains is a classic example of a terminal moraine. A moraine is formed as ice and water melt, pushing earth and rock debris in its path. The Boy Scout Camp was built on ground that was formed over time by a massive glacier.

Before the mountains were glaciated the area was part of a metamorphic and igneous complex that was buried below the crust. They were exposed due to uplift and crustal extension, according to a report put out by the Nevada Bureau of Mines and Geology. This type of thrusting probably ended during the Cretaceous Period, about 144 to 65 million years ago.

U.S. Forest Service geologist Jenna Padilla talked about the most recent ice age that occurred about 2.5 million to around 11,000 years ago.

“The world went through the last glaciation intervals during the Pleistocene,” Padilla said. “There are two glaciation events that have occurred in the Ruby Mountains. The first is known as the Lamoille Glaciation Period and the other is the Angel Lake Glaciation Period.”

“The timeframe from the Lamoille glaciation seems to be pretty argued,” Padilla said. “Some associate this with the Illinoian Stage (about 191,000 to 130,000 years ago) within the Pleistocene. The Angel Lake Glaciation is from the Wisconsinan Stage (about 75,000 to 11,000 years ago).”

Before the last glaciation took place, rock in Lamoille Canyon was limestone at the bottom of the ocean, according to Padilla. The rock was compacted into layers.

“That happened millions of years ago,” Padilla said. “Then fast-forward to a different time when you have tectonics coming in. They produced an uplift coming from the mantle. With heat and pressure the rocks are crunched, creating new metamorphic rocks.”

Padilla is from New Mexico and feels very privileged to be working here and studying the area.

“I think Lamoille Canyon is pretty incredible because the valley features are so dramatic,” Padilla said. “They are perfect examples of how valleys are formed. You have the u-shaped valleys that the glaciers formed and the v-shaped valleys that come from the streams. It is a lot of fun taking kids out there.”

Highway Hoodoos

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Rockin’ the past: Northeastern Nevada’s geologic mysteries

The Carlin hoodoos along Interstate 80 have eroded over time.

The Carlin hoodoos stand like sentinels along Interstate 80. Geologists believe these formations are harder versions of the rock that encased them, which was eroded away by water and wind.

“When the Humboldt River was at a higher level before it eroded down to its current level there were alluvial fan deposits shedding down,” McFarlane said. “The river partially eroded them after they solidified, leaving the hoodoos behind.”

“The Carlin Canyon unconformity is a classic geologic locality where two orogenic events are preserved,” wrote Steven Dutch of the University of Wisconsin. “Early Paleozoic layers were tilted, eroded, then they were overlain by late Paleozoic layers. Then the rocks were tilted again. The early Paleozoic layers are now vertical and the mid-Paleozoic unconformity is now steeply tilted.”

Dutch described the hoodoos as being vertical Cambrian conglomerate layers. In some places they contain siltstone and chert.

Now they inhabited by swallows and on long trips back from Reno serve as a reminder that you are almost home.

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