The most breathtaking sight inside Yellowstone Park is the Grand Canyon of Yellowstone. Twenty miles long, the canyon is up to 4,000-feet wide and 1,200-feet deep in places.
Charles Cook explored the area in 1869, and is credited with discovering the canyon. According to Lee Whittlesey’s Yellowstone Place Names, Cook was said to have commented: “I sat there in amazement, while my companions came up, and after that, it seemed to me that it was five minutes before anyone spoke.”
The canyon, located below Lower Falls, is in a former geyser basin created by rhyolite lava flows, heat and faulting. Chemical and heat action resulted in hydrothermal changes that today can be seen in the form of active geysers and hot springs. It is believed that at the end of the last glacial period melting ice dams at the mouth of Yellowstone Lake caused catastrophic flooding and erosion that led to the formation of the canyon as it exists today.