Yellowstone National Park is 145 years old today! On this day, March 1, 1872, President Ulysses S. Grant established and set aside the Greater Yellowstone Valley as our first National Park. In it's early days, Yellowstone was actually managed by the US Army who established Fort Yellowstone in 1891 near Mammoth Hot Springs. It wasn't until later, that Teddy Roosevelt pushed for the preservation of our National Parks with the Antiquities Act of 1906.