MOOSE, Wyo. — Jackson Hole and Grand Teton National Park (GTNP) are famous for the wildlife in the region, but it’s the geology that made such a diverse ecology and its long-term preservation possible.
While the Teton Range is the most recent geological addition to the Rocky Mountains, these local peaks are still exposing some of the oldest rocks in Wyoming that actually date back billions of years.
“It is fair to say that the core of the Teton Range, the Grand, Middle, South, Buck, most of Mount Moran, is on average 2.6 billion years old,” Mike Scher, Geologists of Jackson Hole (GJH) board member, tells Buckrail. Scher notes there are still rocks in North America that are older, around four billion years old.
According to Scher, the Tetons were raised by 7 to 7.5 magnitude earthquakes triggered on the Teton Fault, which caused the mountain block to tilt upwards and the valley block to tilt down. The exact age of the Teton Range, however, is still debated.
“There is disagreement among earth scientists about when the initiation of movement on that Fault started happening,” Scher explains. “The range goes from about 10 million years to about four and half million years. All of us look at the same data sets, but we interpret them differently and we come to different conclusions. I feel, along with some people that I really trust, that four and a half is a better number. But it is still an area of active research.”
Scher also points out there was a mountain range here before the Tetons; the Tetons are actually part of the Gros Ventre uplift, which is a 65 million year old uplift including the Gros Ventre mountains, today’s Tetons and even some area to the north and west. He says the Teton Fault was then imposed or imprinted on this physical area around 60 million years later.
While the region has been in a quiet stage for the Teton Fault over the past 5,000 years, the 1959 magnitude 7.3 earthquake just outside the boundary of Yellowstone National Park and the 1975 magnitude 6 earthquake is evidence that the whole area is still geologically active. Scher says this means it’s prone to earthquakes and Yellowstone is probably not done erupting. However, he suggests there may never be another caldera-forming eruption, and if there is it could be half a million years from now.
Being a geologically active region also means that the Tetons are still being built.
“The first round of mountain building happened, and now we are living in the second round of mountain building,” Scher says.
Between then and now, Scher also confirms the Ice Age shaped the mountains and ecology here over the last two and a half million years. He says ice has come into the valley and carved out canyons like Paintbrush and Cascade approximately 10 times, including when the Yellowstone Ice Cap came down on the east side of the Teton Range. This is what Scher credits made the purchase and establishment of GTNP possible.
Scher tells Buckrail that when the Yellowstone Ice Cap and Teton glaciers melted, it washed out all the fine grains that were in the soil. This outwash is also what makes the east side of the Tetons less agriculturally rich than the west side; over where Teton Valley is, there was no ice cap washing away the small particles that could hold water and allow plants to thrive, which is why alfalfa, potatoes and more can still be grown there today.
Because of that lack of agricultural potential on the Jackson Hole side, with the exception of grazing, Scher suggests it was possible to create a national park because the land didn’t have a high profitability for farmers or ranchers, in addition to its lack of mineral resources. The National Park Service itself writes in its history chronology that national park boundaries were indeed typically chosen when they encompassed only landscape features considered valueless for lumbering, mining or agriculture.
“The reason the national park is here is because of the geology,” Scher says. “And the ecology is dependent on the geology.”
Scher points out that the reason there are herds of pronghorn and bison here is because of the sagebrush habitat that was only possible because of the drainage patterns from glaciers. Similarly, the moraines, which are the accumulation of debris that occur on the sides of the glacially formed regions, provide tree habitat along with river areas that allow birds and small mammals to thrive in the landscape as well.
Geology also drives the economy, both at a statewide level, with coal and oil production, and at a local level, with tourism.
“The reason that there’s tourism is that you have two big national parks, and the only reason these parks exist is because of the geology,” Scher emphasizes.
But Scher reminds community members and locals alike that a geologically active region warrants both admiration and vigilance. While some of the geological impact is less than others, the landslide on Sheep Mountain in the 1920s or the Budge landslide in 2014 are examples of how geology in action can sometimes have consequences for communities.
“These things haven’t stopped occurring,” Scher says. “They occur all the time.”
GJH will be hosting two free educational events at the Teton County Library (TCL), on Nov. 7 and Dec. 5, where the public can learn about the geology of the area and related topics. More information about these public programs can be found on the TLC website or the GJH page.
