Walnut Canyon National Monument Walnut Canyon National Monument is a United States National Monument located about 10mi north east of Flagstaff, Arizona. It is located next to Interstate 40. It was established in 1915. The canyon rim lies at 6690 ft the canyon floor 350 ft lower. A 0.9 mi long loop trail descends 60 ft into the canyon passing 25 cliff dwelling rooms constructed by the Sinagua people.