Scientists Have a Bold New Theory About How the Grand Canyon Was Formed
The Grand Canyon has been leaving people speechless for as long as people have been looking at it. Theodore Roosevelt stood at the rim in 1903 and said he couldn't find words — that no outsider could truly grasp what they were looking at.
The how and when of its creation has been just as elusive as the words to describe it.
A new study published April 16 in the journal Science is putting forward a theory that reshapes what scientists thought they knew about the canyon's origins — and it involves an ancient lake overflowing in a moment that set everything in motion.
What the Study Says
Scientists have known for a while that the Colorado River existed in western Colorado around 11 million years ago and that it didn't exit through the Grand Canyon until after 5.6 million years ago. What nobody could explain was where the river went in between those two points — a gap of roughly five and a half million years that left scientists largely in the dark.
Now they think they have an answer.
According to study coauthor Ryan Crow of the U.S. Geological Survey, the Colorado River spent that intervening period flowing into something called the Bidahochi basin — a geologic depression in northeastern Arizona that once held large ancient lakes. Starting around 6.6 million years ago, sand deposits in that lake started showing a clear Colorado River signature, indicating the river was feeding directly into it.
Then, roughly 5.6 million years ago, that lake overflowed.
The researchers believe that spillover event is what forced the Colorado River to begin carving what would eventually become the Grand Canyon — linking a series of closed basins together as each one filled and spilled into the next. About two million years after that initial overflow, the lake no longer existed and the Colorado River system had fully integrated all the way to the sea.
"Although parts of Grand Canyon may have been partially carved by other river systems, it was the Colorado River that linked them together," Crow said.
Not Everyone Is Convinced
The study is being described by some as a significant leap forward in understanding one of geology's most debated questions. Others are more cautious.
Karl Karlstrom, a Grand Canyon history expert at the University of New Mexico, said the key details of the spillover conclusion remain untested by the data presented in the paper. The timing, location, and evidence for the lake spillovers are still largely unknown, he argues.
"Thus, the key details of the proposed spillover conclusion remain untested by data presented in their paper," Karlstrom said.
That's the honest reality of this kind of research — the Grand Canyon is ancient, the geological record is incomplete, and piecing together what happened 5 or 6 million years ago involves a lot of educated interpretation. The spillover theory may turn out to be right. It may turn out to be part of the story. Or new evidence may complicate it further.
Why This Matters
The Colorado River of 2026 looks nothing like the water system that carved the canyon. What this research is slowly revealing is that the formation wasn't a single dramatic event — it was a long, winding process where a river kept filling basins, spilling over, linking with the next one, and grinding deeper over millions of years until something vast and irreplaceable emerged from the Arizona rock.
Roosevelt was right that there are no words for it. But at least now there's a better theory for how it got there.
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