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.
[...]
One obstacle in the ancient river's path is the Kaibab Arch, a topographic high point located in northern Arizona and southern Utah. Geologists have proposed different scenarios for how the river crossed it, but one theory that the new evidence makes more plausible is lake spillover. In this scenario, the Colorado River would have filled a lake and eventually exited it along a course to the Grand Canyon.
[...]
The collaborative work began when He, Douglass and Emma Heitmann at the University of Washington met in the field while studying the remnant deposits of Bidahochi Lake, an ancient lake on Navajo Nation land. Most of the deposits of this enigmatic lake have eroded away, so no one knows how large the lake was. Geologists also didn't know what rivers fed the lake, or why Bidahochi Lake eventually disappeared.
[...]
Geologists have developed a technique called detrital zircon geochronology that uses lasers or ion beams to measure the ratios of uranium and lead isotopes in hundreds of zircons in a sample. The unique age and history of each zircon can thus be traced to learn the sources of a sediment and estimate when it was deposited. The age spectrum derived from hundreds of zircons in a sample is called its detrital signature.
[...]
The results showed that signatures of the sediments deposited about 6.6 million years ago in Lake Bidahochi closely matched those of other Colorado River deposits downstream and upstream, including the Browns Park Formation in northern Utah and Colorado.
Study of rock layers in the field from this time period showed signs of rippling that indicated a strong river flowed into standing water, and fossils of large fish species characteristic of fast-flowing waters.
These lines of evidence strongly indicated that the Colorado River was supplying water and sediment to the Bidahochi basin before it spilled over and the river began to flow through the Grand Canyon. This set the stage for the mighty Colorado River that carved much of the Grand Canyon and upon which much of the West depends for water.
From the article:
[...]
[...]
[...]
[...]