Colorado River disappeared record for 5M years: now we know where it was

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Geologists have solved the mystery of the disappearance from the geological record, millions of years ago, of one of North America's most important waterways: the Colorado River. A paper published in Science shows that the river flowed into an upstream lake over the course of a few million years, then likely flowed for the first time into the Grand Canyon. The moment marked the Colorado River's transition to a continental-scale river as it made its way down to the Gulf of California.

"In some ways, you could really think of it as the birth of the Colorado River that we know today," said first author and UCLA geologist John He.

"There are rivers everywhere, but a river that carries water and sediment across the continent connects life throughout the region, and the entire ecosystem probably changed as a result of the arrival of the Colorado River into the basin."

The finding, based on the analysis of sandstone samples, complements paleontological evidence, such as fish fossils, that suggests life began to become part of an integrated ecosystem throughout the Colorado River basin during this hidden chapter of its history.

How and when did the Colorado River reach the Grand Canyon?

The Colorado River existed in western Colorado 11 million years ago and first exited the Grand Canyon around 5.6 million years ago. But how it navigated the terrain between the two points for around 5 million years had been a mystery.

Now, new evidence suggests it pooled just east of the Grand Canyon, in what is now part of the Navajo Nation, before charting a downstream path that ultimately led to the Gulf of California around 5 million years ago.

The Grand Canyon was carved in multiple phases over a long period of time, but precisely when and how much the Colorado River incised it remains debated among geologists.

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