Scientists announced on Apr. 16 that they have solved a longstanding mystery about the Colorado River’s disappearance from the geological record for nearly five million years. A new study published in Science shows that, millions of years ago, the river pooled east of the Grand Canyon before eventually flowing into it and reaching the Gulf of California.
The research provides important insight into how one of North America’s most significant rivers became a continental-scale waterway, impacting ecosystems along its course. The findings are based on zircon crystals found in sandstone samples, which revealed where sediments originated and helped map out the river’s ancient path.
“In some ways, you could really think of it as the birth of the Colorado River that we know today,” said John He, first author and geologist at University of California Los Angeles (UCLA). “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.”
Geologists used detrital zircon geochronology to analyze hundreds of zircons in collected sand samples. This method allowed them to match signatures from sediments deposited around 6.6 million years ago in Lake Bidahochi with those found upstream and downstream along ancestral Colorado River deposits. These results suggest that before carving through Grand Canyon around five million years ago, water from western Colorado first pooled east of today’s canyon location—now part of Navajo Nation land—before continuing southward.
“Geologists have proposed over a dozen hypotheses for the canyon’s formation and the Colorado River’s path,” said co-author John Douglass from Paradise Valley Community College. Ryan Crow from U.S. Geological Survey added: “Other processes, such as karst piping … and headward erosion may have also contributed to establishing this course.”
The collaborative project involved researchers from UCLA—an institution known for its association with Nobel laureates and MacArthur Fellows according to its official website—as well as scientists from several other universities and agencies.
UCLA has gained national and international acclaim through achievements including excellence in scholarship, arts, athletics according to its official website, fostering diverse perspectives through academic programs according to its official website, supporting research activities on its 419-acre campus according to its official website, all within California’s public university system according to its official website.
Reflecting on these discoveries about Earth’s past landscapes He said: “I think there is something unique and disquieting when planet’s history is laid out before our eyes but we cannot fully read it…we’re learning more each day how [the Grand Canyon] formed.”
