About 12,000 years ago a large landslide rumbled down the west side of Dome Mountain and smashed across the Yellowstone River at the southern end of the Paradise Valley.
“It was a pretty catastrophic landslide,” said Jean Dixon, associate professor of Earth Sciences at Montana State University in Bozeman. “It ran up and over the side of the hills and fully dammed that river.”
The slide at the mouth of Yankee Jim Canyon blocked the Yellowstone River, creating a lake that stretched about 14 miles upstream, all the way beyond present-day Gardiner. Where the town now stands would have been prime beachfront property. Estimates by a geologist put the maximum depth of the water close to an elevation of 5,225 feet. Gardiner sits at an elevation of 5,259 feet.
The dam is one example that water and ice, almost as much as fire and volcanoes, have played a large role in sculpting the area in and around Yellowstone National Park. The ancient lakes, dams and floods may be less sexy than a volcano that created a 34- by 45-mile wide caldera — blowing enough ash into the atmosphere to bury the city of Billings under 3 feet of dust — but they still help tell the story of a unique place cherished for centuries by natives, local residents and, more recently, visitors from around the world.
Those visitors may now ride a raft or kayak through the narrow confines of Yankee Jim Canyon, bouncing over waves created by huge boulders, unaware of the geologic history of the place.
The idea of a narrow, winding lake near the North Entrance to Yellowstone National Park may be hard to imagine. But an example of a similar occurrence can be found near the West Entrance to the park, where a large landslide in 1959 created Quake Lake by blocking the Madison River. That slide, triggered by a strong earthquake, dumped an estimated 73 million metric tons of dirt, trees, boulders and gravel into the drainage. Nine people were killed.
One of the first things the government did after the Quake Lake slide was to punch an outlet into the boulders, Dixon said, to avoid a large buildup of water behind the rock dam. Otherwise, the water could have overtopped the slide or burst out, sending a torrent of water downstream, killing residents or flooding homes in the Madison Valley below.
Earlier this year a slow-moving landslide wiped out a forest road and moved across the Greys River in western Wyoming, almost blocking off that stream.
In the 1970s, bureaucrats floated the idea of constructing a dam just south of Livingston, in the narrow canyon that opens up to the Paradise Valley near Carter’s Bridge. The plan, which would have flooded the valley as far south as Emigrant, was eventually halted after environmental groups and conservationists protested the proposal. The Yellowstone River is now the largest undammed river in the United States. Although irrigation dams do dot its length, they do not halt its progress.
Had the dam not been stopped, a large portion of the Paradise Valley would now be underwater. As it turns out, however, nature created its own dam along the river thousands of years earlier.
One of the first people to publish anything about the slide at Yankee Jim Canyon was John M. Good, a Yellowstone National Park geologist. Good wrote a paper in 1982 that estimated the slide originated on the southwest side of Dome Mountain, an area that now includes a well-known elk winter range. He theorized the slide’s toe moved more than 2,000 feet to block the river, with the top of the slide towering 200 feet above the river’s present level.
“It was a paleo Quake Lake,” said Cathy Whitlock, a professor of Earth Sciences at MSU.
For comparison, Canyon Ferry Dam on the Missouri River is 225 feet high.
How long the Yankee Jim dam lasted is hard to calculate, said Ken Pierce, geologist emeritus for the U.S. Geological Survey in Bozeman, who dated the lake based on charcoal he found in sediments gathered near Corwin Springs. It could have been a few years to tens or hundreds of years, he said, probably dependent on how watertight the dam was, since a holey dam wouldn’t build up as much pressure behind it.
“I would expect the dam was kind of leaky,” Pierce said, “because the rockslide that dammed it was made of fairly porous material.”
One thing is for certain: when the dam failed it produced a “torrential flood which swept slide debris into great barlike forms immediately below the slide mass west of the river and left lag deposits of huge boulders east of the river,” Good wrote.
Dixon said visitors to the area downstream of Yankee Jim can still see the weathered remains of huge ripples more than a meter high left by the outrush of water. Angular rocks from the landslide that haven’t been eroded by water are also scattered below the old dam, Pierce said.
Pressure behind the dam must have been enormous. If it measured 200 feet high, that would have translated into about 87 pounds per square inch of pressure. Humans can withstand only about 58 psi when diving underwater without being crushed. Most recreational divers don’t go deeper than 130 feet, according to the Professional Association of Diving Instructors.
Maps show the location of the slide close to where Sphinx Creek enters the Yellowstone River from the west and close to the Canyon Campground on the east. The campground is punctuated by towering boulders that Dixon said were moved there by flooding, not simply by falling from the nearby mountain. The elevation close to that location is about 5,000 feet. Based on Good’s estimate then, the water of the ancient lake could have been 225 feet deep there.
Proof of the Gardiner Basin lake’s existence is also found in the archaeological record near Gardiner, at a site known as Rigler Bluffs, but the dates are much earlier than 12,000 years ago.
At the bluffs site, a rock-lined hearth was excavated about five miles upstream from the ancient dam. The hearth was buried under 8 feet of “former lake silts,” according to a 1966 archaeological survey of the upper Yellowstone River drainage by George Arthur, of the University of Montana.
“That the hearth was buried under at least eight feet of lake silts indicates that it was made when the lake was rising,” Arthur wrote. “This suggests that the slide occurred just prior to the occupation of this site.”
“Thus, an environment was created which was doubtless quite attractive to prehistoric men of the drought-plagued altithermal period,” wrote Yellowstone historian Aubrey Haines, of the Rigler Bluffs site. The altithermal was a warm period about 5,000 to 7,000 years ago.
Further evidence that American Indians may have been present during the large lake’s existence comes from the Carbella archaeological site, located just below where the Yankee Jim dam would have blocked the Yellowstone River. A campsite there is presumed to predate the dam’s failure, since many of the artifacts were scattered as if by a flood.
“This suggests that the slide occurred just prior to the occupation of this site,” Arthur wrote.
Based on the human-made projectile points found at the Carbella site, the ancient campground is estimated to date to between 5,000 and 7,000 years ago.
More recent excavations in 2005 and 2008 of a campsite near Malin Creek, near the mouth of the Black Canyon of the Yellowstone, found lake sediments overlaying the site that dated to about 10,280 years ago.
“This indicates prehistoric people camped roughly 9,400-9,800 years ago on the shore of a lake that no longer exists,” according to a brief history of Yellowstone archaeology posted on the park’s website.
Those archaeological sites, and the Yankee Jim landslide, predate other large floods that swept through the area during glacial times, creating many of the landforms still visible.
The last period of extreme cold in Yellowstone is known as the Pinedale glaciation, dated sometime between 21,000 to 13,000 years ago. By 14,000 to 15,000 years ago, most of Yellowstone was relatively ice-free, Whitlock said.
Pierce said meltwater from glaciation that saturated the soil may have been what weakened Dome Mountain causing the landslide. Dome Mountain was a nunatuk, he said, a Greenlandic word meaning the top of the mountain was just above the northern Yellowstone glacier.
“After those glaciers retreated, you had these unstable formations that were super saturated with water, so there were a lot of landslides,” said Ann Rodman, supervisory GIS Specialist in the Yellowstone Center for Resources.
The most recent northern Yellowstone glaciation would have “completely filled the upper (Gardiner) valley and extended far up on the mountain sides, completely covering such minor elevations as Cinnabar (elevation 7,163), Sphinx (elevation 7,143),” Arthur wrote. That glacier extended all the way past what is now the small town of Emigrant. Pierce estimated the glacier’s starting point to have been around Lower Aero Lake, high in the Beartooth Mountains north of Cooke City.
“Most of the ice was 700-1,200 meters thick and one continuous glacial-flow line, (90 miles) long, was probably the longest glacier in the conterminous United States, except for those originating in Canadian icecaps,” Pierce wrote. He published a comprehensive paper on the glaciation of Yellowstone in 1980.
“The Yellowstone glacial system was entirely homegrown,” Pierce said, “separate from the ice sheets that came down from Canada.”
As the four ice caps covering northern Yellowstone melted, receded and moved, a glacier protruding from the Slough Creek valley advanced downhill and blocked off the Lamar River, creating a lake in the Lamar Valley.
Close to the Northeast Entrance of Yellowstone Park, the Lamar Valley offers a vast, almost Alaskan view of land still populated by bison, grizzly bears and wolves. The Lamar River meanders through the broad swath of land, its corridor dappled by cottonwood trees. But thousands of years ago it was under ice, and then underwater as far up as the Soda Butte Creek drainage.
At least two times the Lamar dam was breached, Pierce estimated, sending torrential floods 150- to 200-feet deep downstream, gushing through the narrow confines of the Black Canyon of the Yellowstone and twice chopping off huge alluvial fans created by other floods emanating from Reese Creek near Corwin Springs.
In that same area near Reese Creek, Pierce wrote, the “most impressive evidence of flooding can be seen,” a midchannel flood bar that dates to about 15,000 years ago. Located on the south side of the Yellowstone River, close to the park boundary, the bar is 65-feet tall and 1,400 feet across with its surface “covered by giant current ripples.” Bowed ridges about 6 feet high and 49 feet apart “trend across the bar. Boulders up to 6 feet in diameter cover the ridge crest.
Pierce explained that once the Lamar lake’s volume rose to nine-tenths the height of the ice dam, the ice would have floated up, releasing water underneath.
In comparison to these glacial floods, the Yankee Jim outburst would have been much smaller, “about half as high as the highest late Pinedale flood,” Pierce wrote.
It’s hard to confirm whether Paleo-Indians may have witnessed the Lamar lake flood. The dating of an ancient burial site in the nearby Shields Valley, where artifacts and the remains of two children were uncovered in 1968, has produced a timeframe of human habitation of the area 12,750 to 12,900 years ago.
A study of animal remains found in a cave in the northern Yukon has pushed back human occupation in that region to 30,000 years before present. Perhaps Paleo-Indians were in Montana between these dates.
Archaeological and geological evidence does confirm that Paleo-Indians were present when the Yankee Jim landslide occurred and the Gardiner Basin flooded, creating a Paleo Quake Lake. Such dams, as noted earlier, aren’t rare. A 1991 USGS report documented more than 460 such landslide dams just in historical times, and the authors note that their report isn’t comprehensive.
Dixon often takes her MSU Earth Science students on field trips to the Gardiner Basin and Yankee Jim Canyon to see the remains of the landslide, the lake it produced and the catastrophic flood that would have shot out of the canyon when the dam gave way.
“It’s a pretty cool story,” she said.