Grand Canyon much older than previously thought The Grand Canyon, carved out over the eons by rushing river water, began to form 17 million years ago, making it nearly three times older than previously thought, scientists said on Thursday. The general consensus among geologists had been that the famed natural landmark in Arizona was about 6 million years old. But now University of New Mexico scientists say it is far older based on their findings using a technique called uranium-lead isotope to date mineral deposits in caves from nine sites in the canyon's walls. The cave formations provided a record of a dropping water table as the canyon deepened. The gorge is 277 miles long, 1.1 miles deep at its deepest point and up to 18 miles wide. The Colorado River that runs through it arises in the Rocky Mountains of Colorado and flows southwest about 1,400 miles to the Gulf of California. The scientists found that there is a kind of dual history to the canyon, with the western portion starting to form about 17 million years ago when water from a predecessor to the Colorado River began the slow, inexorable process of eroding the rock, they said. The eastern portion began forming closer to the 6 million-year-old date that had been the estimate for the whole canyon, they said....