how big is it?
thermochronometry showws that it  reached a depth near to the modern depth by 20 Ma
Grand Canyon
The Grand Canyon is part of the Colorado River basin which has developed over the past 70 million years, in part based on apatite (U-Th)/He thermochronometry showing that Grand Canyon reached a depth near to the modern depth by 20 Ma. A recent study examining caves near Grand Canyon places their origins beginning about 17 million years ago. Previous estimates had placed the age of the canyon at 5–6 million years. The study, which was published in the journal "Science" in 2008, used uranium-lead dating to analyze calcite deposits found on the walls of nine caves throughout the canyon. There is a substantial amount of controversy because this research suggests such a 
what is the second layer of the grand canyon made of It is made up of nearly 40 major sedimentary rock layers how many layers are there? 40 layers how did this form? By deposition  in warm, shallow seas and near ancient, long-gone sea shores in western North America. do the layers have any names? One of them is the Vishnu Basement Rocks where is this canyon located? Arizona, United States.
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Grand Canyon [SEP] Geology
The Grand Canyon is part of the Colorado River basin which has developed over the past 70 million years, in part based on apatite (U-Th)/He thermochronometry showing that Grand Canyon reached a depth near to the modern depth by 20 Ma. A recent study examining caves near Grand Canyon places their origins beginning about 17 million years ago. Previous estimates had placed the age of the canyon at 5–6 million years. The study, which was published in the journal "Science" in 2008, used uranium-lead dating to analyze calcite deposits found on the walls of nine caves throughout the canyon. There is a substantial amount of controversy because this research suggests such a substantial departure from prior widely supported scientific consensus.