Washington: Geologists have found evidence
of a giant river which flowed in the opposite direction some 55 million years ago in the same region where the present-day Colorado River is carving the famous Grand Canyon in the US.
Researchers at the Carnegie Institution of Washington
discovered the ancient river system by comparing sedimentary
deposits in Utah and southwest Arizona.
By analysing different types of uranium and lead atoms in
sand grains made of the mineral zircon, they were able to
determine that the sand at both locations came from igneous
bedrock in the Mojave region of southern California.
According to the researchers, zircons with the same lead
and uranium signatures were found in both old river sediments
in northern Utah as well as rocks southwest Arizona.
This means there had to be a mighty river to carry the
minerals about 700 km northeast, the Discovery News reported.
It appears that the ancient river, named the California
River, could have started in Mojave Desert of southeast
California and southwest Arizona and headed northeast all the
way to northern Utah, some 55 million years ago, said the
But it wasn`t enough to just find the zircons, said Steve
Davis, the lead author of the study which is published in the
"We had to prove how sure we were that they didn`t come
from the same place," said Davis.
They failed to statistically disprove the connection
between the distantly placed zircons and reached the opposite
conclusion that the rocks are originally from the same place
and those in Utah were carried by a long river.
"Zircons are very resistant to weathering and so can
travel a long, long way," commented geologist Christopher
Henry of the University of Nevada in Reno and the Nevada
Bureau of Mines and Geology.
"That`s why they are handy in reconstructing the ancient
lay of the land. Basically I`d say these people are right."
The source of the zircons appears to be granite-like
rocks in what were called the McCoy Mountains, the remains of
which are in southwest Arizona. This would have been part of
the headwaters of the California River, the experts believe.