There are a variety of ideas regarding how the Grand Canyon was formed. It is widely agreed that the Colorado River formed most of it, carving the canyon over millions of years with the help of plate tectonics, geologic uplift, and erosion from wind, rain, and ice. What has yet to be agreed upon is the certain age of the Colorado River- which would shed light upon the age of the Grand Canyon itself.
Traditional geologists of the 1950’s believe the canyon to be more than 70 million years old. They suggest it was formed at the beginning of the Tertiary. The mid-western regions of Colorado, Utah, and Arizona were a mere 1,000 feet above sea level and very hot and humid. Rivers ran wild and abundant. Plate tectonics formed mountain ranges at convergent boundaries which would weather away over millions of years and scatter gravel deposits over the land causing uplift. Over the last 5 million years, the climate changed to the desert of today and the Ancestral Colorado River all but dried up, moving underground or sporadically during seasons of moisture.
Recent geologists, however, have a different idea of how the Grand Canyon was formed—having only formed over the last 5 million years. There seems to be no substantial evidence of the old river system and lakes that would feed the Colorado River of today. While the upper portion of the Colorado River strikes geologists as very old, the sediment of the lower river portion is incredibly new. This leads many geologists to believe the Ancestral Colorado River used to flow a different course, but at some point in the last 5 million years, that course was disrupted and cut off. Then a separate river from the west, that has yet to be named, joined up with the Ancestral Colorado and this new river system was responsible for how the Grand Canyon was formed.
