AZGS scientists contribute to breakthrough study on Colorado River and Grand Canyon history
At Roberts Mesa the contrast between the dark red mudstone beds and the tan sand-dominated layers above marks the arrival of Colorado River sediment into the Bidahochi Basin 6.6 million years ago. This set the stage for the integration of the Colorado River and the formation of the Grand Canyon. Drone image courtesy of Brian Gootee. Note: Any person(s) wishing to conduct unmanned aerial vehicle flights on the Navajo Nation must first apply for and receive a permit from the Navajo Department of Transportation.
The Colorado River and the Grand Canyon are icons of the American Southwest. For decades, geologists have worked to uncover the history of the river and the formation of the canyon. A paper published today in Science, coauthored by AZGS Research Scientists Brian Gootee, Phil Pearthree, and Kyle House, reveals a key piece of this history: a precursor to the formation of the Grand Canyon.
Sand collected on March 30, 2023, from exposures in the upper Bidahochi Formation (seen in the background) in northeastern Arizona. AZGS Research Scientist Brian Gootee commented at that time that this sample looked identical to the Colorado River sand in Lower Colorado River basins downstream of the Grand Canyon. That observation ultimately led to the research and findings presented in this paper. Photo courtesy of Brian Gootee.
“This study comes on the heels of many years of research on the Lower Colorado River led by Kyle House, Phil Pearthree, Jon Spencer, Ryan Crow, and others,” said Brian Gootee. “They found that the Colorado River arrived suddenly in the area below the mouth of the Grand Canyon by about 5 million years ago, and filled successively lower lake basins before reaching the Gulf of California by 4.6 million years ago. That finding led us to ponder what was happening upstream of the Grand Canyon, prior to the development of the Lower Colorado River.”
Efforts led by Gootee and John Douglass of Paradise Valley Community College over the last 20+ years led to a new focus on sediments in the Bidahochi Basin, located upstream of the Canyon in northeastern Arizona.
The current team, led by John Douglass, John He of UCLA, and Ryan Crow of the US Geological Survey, succeeded in identifying the signature of Colorado River sediments in the Bidahochi Basin for the first time.
Specifically, they analyzed thousands of zircons, which are tiny mineral grains that persist for millions of years in sediment deposits, preserving information about their age and source area. The zircons in the Bidahochi Basin matched those previously identified downstream as the early version of the Colorado River.
The presence of Colorado River sediments in this region suggests that the river deposited water and sediment into a large lake east of the modern Grand Canyon, forming a delta ecosystem before eventually overflowing and beginning to carve the canyon between 6 and 5 million years ago.
A key component of this rich scientific finding was collaboration between multiple institutions: scientists at UCLA, AZGS, USGS, and three other colleges and universities came together for the investigation.
The findings build off long-standing relationships between many of these scientists, highlighting both the complexity of this geological story and the excitement of gradually putting the pieces of this history together.
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