Study Dates Grand Canyon Carving to 5.6 Million Years Ago

New geological research has revealed that the Colorado River began carving the Grand Canyon around 5.6 million years ago after pooling into a vast ancient lake in northern Arizona, filling a critical gap in the river's prehistoric path.

The study, published this week in the journal Science, draws on analysis of microscopic zircon crystals in sandstone deposits and volcanic ash layers from the Bidahochi Formation. Researchers from the University of California, Los Angeles, the U.S. Geological Survey and other institutions traced sediment origins to show that the river first entered the Bidahochi Basin in northeastern Arizona about 6.6 million years ago. There, it formed a shallow lake spanning more than 90 miles, much of it on land now part of the Navajo Nation reservation. Over time, the lake's waters rose and spilled westward over a low point on its rim, directing the river through the region that would become the 277-mile-long Grand Canyon.

This spillover event initiated the river's modern course, allowing it to incise deeply into the landscape. Downstream, the river filled and overflowed additional basins before reaching the Gulf of California in northwestern Mexico around...