This piece is part of a special project on deep time examining what the Western U.S. was like thousands, millions and even billions of years ago, and how that history is still visible and consequential today. Read more stories from the series.
The Colorado River flows through Marble Canyon in jade-colored plumes, snaking through narrow terracotta cliffs. This is the stretch of the Grand Canyon where rafters begin their journeys. After launching at Lees Ferry, Arizona, and rounding the next bend, they find themselves surrounded by little more than rock and wind. Nothing in this quiet corridor hints that it once lay submerged beneath an enormous lake.
Had you been rafting Marble Canyon 56,000 years ago, you might have looked up and seen something strange growing larger in the sky: An asteroid streaking across the horizon and slamming into the desert about a hundred miles southeast, punching a gaping hole known today as Meteor Crater.
Now, in a recent study published in Geology, retired University of New Mexico geologist Karl Karlstrom and his colleagues conclude that the asteroid’s impact shook Marble Canyon hard enough to dislodge great chunks of stone and send a landslide tumbling into the river. The debris formed a natural dam that backed up the Colorado for over 50 miles to near present-day Lees Ferry. The water swelled to the size of today’s Lake Mead, flooding canyons and caves, leaving traces nearly 300 feet above the modern river.
When Arizona Geological Survey geologist Kyle House first read the study, he thought: “No way. How could it have taken this long to figure this out?”
IN THE 1960s, Karlstrom’s father, also a geologist, and several other scientists entered Stanton’s Cave, 32 miles downstream of Lees Ferry. Inside, they found loose sediment and driftwood nearly 150 feet above the river. Later, U.S. Geological Survey geologist Richard Hereford developed a hypothesis: Something must have dammed the river, forming a lake. But with just the Stanton’s Cave evidence and a squint-to-see-it possible ancient dam site 20 miles downstream at Nankoweap Canyon, the younger Karlstrom “never believed (Hereford’s) story, frankly.”
Then, in 2019, researchers in Australia and New Zealand reanalyzed the driftwood using modern techniques, pushing its age from 43,700 years old to about 56,000. That number raised eyebrows: One of the collaborating scientists had stopped at Meteor Crater on a road trip months earlier and watched a visitor-center film. He remembered the timing of the impact — also about 56,000 years ago.
The team asked Karlstrom, who had spent decades studying the canyon, to help them research the connection. As they sifted through Marble Canyon’s caves, many of which Karlstrom knew from guiding river trips in the 1970s, he came around on the lake hypothesis: The sediment-choked nooks and crannies sat at elevations that could only be explained by a large lake. However, establishing a clear link to the meteor impact was another matter.
LIKE LAWYERS ARGUING a case, researchers must establish overlapping timelines to link prehistoric events. But that’s not as simple as tossing a rock into a machine and reading off an age. Working in deep time requires a large toolkit, with each tool tuned to different slices of Earth’s history.
Radiocarbon dating is a tried-and-true method for material up to about 50,000 years old; any older, and the signal fades. “We were pushing the limits,” Karlstrom said of the driftwood’s age. So the team added luminescence dating of cave sediment, which revealed the time elapsed since it last saw sunlight. Those ages overlapped, within error, with the ages of both the driftwood and the crater, which was also dated using multiple methods.
“They do make a pretty strong case,” said Ryan Porter, a geologist at Northern Arizona University who was not involved in the study. But the aligned ages alone can’t rule out other landslide triggers, he said, like an earthquake or the canyon shedding a cliff on an ordinary day. Still, when asked whether a meteor impact could have rattled the Grand Canyon enough to set off a landslide, Porter didn’t hesitate: “Oh, 100%. There’s no question about that.”
The authors concede that other explanations for the dam are possible, but outside experts agree that the driftwood wasn’t carried in by a flood or left behind as the canyon was excavated. “In geology, you don’t absolutely prove,” said Karlstrom. “You eliminate other possibilities.”
“In geology, you don’t absolutely prove. You eliminate other possibilities.”
THIS IS HOW that day might have unfolded. When the asteroid slammed into the Kaibab Limestone, the same formation that rims the Grand Canyon, the shaking was equivalent to a magnitude-5.4 earthquake. Shock waves rippled to Marble Canyon, weakening to about magnitude 3.5 — still strong enough to have dislodged Kaibab blocks and debris, damming the Colorado River at Nankoweap Canyon. The water then slackened and began to fill its narrow container.
Today, Glen Canyon and Hoover dams provide a vital lifeline to the parched Southwest. But no dam lasts forever. Sediment chokes reservoirs, surging water erodes barriers. For now, how long the ancient dam endured, and how, exactly, it failed — suddenly or otherwise — remain mysteries, evidence that the long geologic story of the Grand Canyon still holds
many secrets.
We welcome reader letters. Email High Country News at editor@hcn.org or submit a letter to the editor. See our letters to the editor policy.
This article appeared in the January 2026 print edition of the magazine with the headline “The crater and the canyon.”
Republish our articles for free, online or in print, under a Creative Commons license.
