While it is impossible to date the Grand Canyon definitively, the national park turned 95 a couple days ago. President Wilson signed the park into being on February 26, 1919. Teddy Roosevelt had visited the park in 1903 and declared it one of the greatest natural wonders of the world.
Hard to argue when you see this incredible site, as I did a few years back with my family. Hiking down to its base takes some planning as there is a waiting list, but you can circumnavigate the rim by car, camping along the edges and taking short walks down some defined trails. Not so long ago, a skywalk was created for those who want to look down between their feet into the canyon.
The canyon was first called to Americans' attention by John Wesley Powell in 1869, when he led a geographic expedition down the Colorado River. He was a prime advocate of water management in the West, but unfortunately no one paid much attention to him, otherwise we might not have seen the many problems that exist today. His book, The Exploration of the Colorado River and Its Canyons is a must read.