How old is the Colorado River?
Five to six million years — which sounds ancient until you put it next to a dinosaur. The last dinosaurs died 66 million years ago. The river is more than 11 times younger than that. Not one dinosaur ever drank from it, because it was not there.
Real photograph · 301520401/Shutterstock.com · Shutterstock Standard (free image collection, API) License
The canyon is young. The rock is not.
“Finally, beginning just 5-6 million years ago, the Colorado River began to carve its way downward.”
U.S. National Park Service, Grand Canyon National Park — Geology.
“Even the youngest rock layer, the Kaibab Formation, is 270 million years old, many years older than the canyon itself.”
U.S. National Park Service, Grand Canyon National Park — Geology.
That is the thing worth holding on to. The Grand Canyon is a young cut through very old rock. The stone at the very top of the canyon wall was already 264 million years old before the river started work on it, and the stone at the bottom is far older still.
So no dinosaur drank from it
Line the two up. Dinosaurs: gone by 66 million years ago. Colorado River: starts cutting 5 to 6 million years ago. There are about 60 million years between the last dinosaur and the first Colorado River.
People imagine dinosaurs drinking from the rivers we know, and it is a lovely picture, and it is wrong for this one. Rivers are not permanent. They start, move, capture each other and vanish on timescales far shorter than the animals we like to put beside them.
The water, though, is a different story. That is much older than the river and much older than the dinosaurs, and it has been round the cycle more times than anyone can count — how old is the water on Earth?
AI reconstruction — not a photograph · Shutterstock AI/Shutterstock.com · Shutterstock Standard License
And the biggest question is still open
“Perhaps the biggest question of all, how the Colorado River chose this course and began carving the Canyon, still awaits a clear answer.”
U.S. National Park Service, Grand Canyon National Park — Geologic Formations.
That is the National Park Service, on its own most famous canyon, saying nobody has settled it. Not a gap in what you have been told — a gap in what is known. Those are worth noticing, because they are where the work still is.
For teachers
For school
- The Grand Canyon is a young cut through very old rock.
- There are about 60 million years between the last dinosaur and the first Colorado River.
- Rivers are not permanent. They start, move, capture each other and vanish on timescales far shorter than the animals we like to put beside them.
Classroom prompt
Draw a timeline and mark three things on it: the Kaibab Formation, the last dinosaurs and the moment the Colorado River began to carve. Which two are closest together, and does that surprise you?
Extension: the National Park Service says how the river chose its course “still awaits a clear answer”. What is the difference between a gap in what you have been told and a gap in what is known?
Ages: “the river is younger than the rock” works from about seven; the timeline and the subtraction suit pupils of about nine upwards. That range is our teaching choice for this page, not a curriculum claim.
Where this comes from
- The quotations
- U.S. National Park Service, Grand Canyon National Park — Geology and Geologic Formations, read . Material created by the National Park Service is generally in the public domain. The date of the extinction is the same figure this site uses everywhere, cited to the International Chronostratigraphic Chart.
- How sure is this?
- “Five to six million” is a range because the reconstruction gives a range, and the source itself says the bigger question of how the river got there is unresolved. The arithmetic on this page is simple subtraction between two published figures; it inherits their uncertainty and adds none of its own.
Where next
Another river that turns out to be younger than people guess is the Mississippi, whose valley was cut by melting ice. For the opposite end of the scale, read what is the oldest river on Earth? — and every river on this site is on the rivers page.