Hells Canyon, the deepest river gorge in the United States, has long captivated scientists and adventurers alike.
New research suggests that this formidable canyon was rapidly carved approximately 2.1 million years ago due to significant geological shifts in Idaho that led to a colossal lake overflowing.
This revelation arose from a study that investigated ancient river sediments long hidden in caves within Hells Canyon, which today stand high above the contemporary Snake River.
Darryl Granger, a geoscientist at Purdue University not involved in the research, praised the study, calling it “brilliant” for utilizing caves to date the enigmatic canyon, which has puzzled geologists for over a century.
“[They had] the persistence to find the right caves that still had river sand and gravel inside, just as it was deposited millions of years ago,” Granger states.
Hells Canyon straddles the border between Oregon and Idaho, reaching depths of nearly 8,000 feet—making it significantly deeper than the iconic Grand Canyon in Arizona, which has a maximum depth of around 6,000 feet.
Despite its impressive depth, Hells Canyon has not captured as much scientific interest as the Grand Canyon, as noted by Matthew Morriss, a geologist with the Utah Geological Survey, who became interested in the canyon at the age of 19 during a college field trip.
During that visit, he was stirred by a curiosity about the canyon’s origins, prompting multiple subsequent explorations, which included challenging hikes and encounters with poison ivy.
Morriss searched for evidence that the ancient river once flowed through the canyon, a task that involved looking for sediment deposits left behind as the river profoundly modified the landscape.
Typically, canyons may have flat terraces where rivers leave behind sediment, but Hells Canyon’s steep rock walls lacked these features.
Thus, Morriss turned his attention to limestone caves that might have once contained sediment-laden water as the river carved its path through the gorge.
Supporting evidence that has led to dating efforts in other river canyons indicated that this method could work in Hells Canyon, provided the right conditions were met.
With the help of knowledgeable local spelunkers, Morriss embarked on a search for appropriate caves in Hells Canyon.
Upon entering the very first cave on their expedition, they discovered an abundance of gravel, which was then sampled for analysis.
This initial success led to further exploration of over 30 additional caves, where they found more ancient river sediments.
Subsequently, the research team employed a sophisticated dating technique on the gravel samples to establish how long it had been since the river deposited these minerals in the caves.
The cave settings protected the minerals from cosmic rays, which could have altered their chemical composition over time, ensuring accurate dating.
The results, which were published in the Proceedings of the National Academy of Sciences, confidently assert that Hells Canyon began developing 2.1 million years ago, when no river canyon existed prior to that time.
The prevailing theory posits that the canyon’s formation was triggered by the draining of a massive lake that once encompassed much of what is now Idaho.
Geological changes and glacial melting led to an increase in runoff into this lake, culminating in a “fill and spill” event that provided the necessary water to sculpt Hells Canyon.
Morriss expressed surprise at the canyon’s relatively youthful age, noting it’s actually younger than the Grand Canyon; stretches of the Grand Canyon are estimated to be about 5 million years old.
As he concluded the research, Morriss felt a sense of satisfaction in answering the questions that had piqued his curiosity as a teenager during that fateful field trip.
“[It was] nice to put that to rest and also be able to email my college professors and say, ‘See, I told you I’d find out how old this was,’” he reflected, excited about sharing the findings with his mentors.
With its newly established age, Hells Canyon not only reveals the dynamic geological history of the region but also enhances our understanding of the landscape that shapes our natural world.
image source from：https://www.npr.org/2025/05/27/nx-s1-5409017/hells-canyon-deepest-gorge-young-grand-canyon
