ST. GEORGE — Sediment deposits often line the walls of river channels and lakes. For geologists, these deposits contain the keys to prehistory’s most elusive secrets.
Evidence from deposits along the lower Colorado River suggests that the region was once the site of a succession of lakes as the river pushed southward from what is now the Hoover Dam toward the Gulf of California, according to a paper by a team of geologists that earned them the Geological Society of America’s prestigious Kirk Bryan Award for Research Excellence.
The team includes Michael Perkins, adjunct assistant professor of geology and geophysics at the University of Utah. The paper was co-authored by Phil Pearthree of the Arizona Geological Survey and Kyle House of the U.S. Geological Survey. The authors will be honored at the GSA Annual Meeting and Exposition award ceremony in Denver, Colorado, on October 28.
The paper is the latest contribution to the field in answering a question that has baffled geologists for a century: Why and how did the lower Colorado River take the form that it did?
About 5.6 million years ago, the 2007 paper proposed, the Colorado River swelled with an influx of water, which made the river fill basin after basin in its push southward. The river formed a lake in each and left sediment deposits. Each lake marked the river’s final extent for some time until the basin was filled to the point of breaching the rim, at which point the river continued its course, spilled into the next basin, and repeated this process.
The geologists further stated in their paper that the river took a couple of million years to forge the less than 400-mile course that today comprises the border between California and Arizona.
Evidence for the findings was derived from an examination of the sequence and distribution of sediments within river channel and lake deposits in the Cottonwood and Mohave Valleys near Bullhead City in the lower Colorado River Valley. The one-time existence of lakes that filled the basins along the river’s path is corroborated by the presence of fine-grained mudstone and limestone deposits.
Since 1958, the Kirk Bryan Award has been bestowed annually upon the author or authors of a published paper of distinction that advances the science of geomorphology or a related field.
Founded in 1888, the GSA is the oldest professional Earth sciences scientific society in North America. GSA has more than 25,000 members in over 103 countries. The Society’s chief functions include hosting scientific conferences and workshops, publishing scientific literature, acknowledging and trumpeting excellence in the geosciences, and science outreach to the broader public.
For more information on the award ceremony see page 15 of the July issue of GSA Today.
Contact: Michael Conway, Arizona Geological Survey, 416 W. Congress, Ste 100 Tucson, AZ 85701 / Telephone 520.209.4146 / Email Michael.Conway@azgs.az.gov
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