Glen Canyon Dam is a concrete arch dam constructed on the Colorado River in  the far north of Arizona. It is named for its location in the gorge known as Glen Canyon, now largely submerged, where the river enters Arizona from Utah. The dam backs up the river to form a reservoir, named Lake Powell, extending far back into Utah. Below Glen Canyon Dam, the Colorado River flows freely for 370 miles before encountering the next dam, Hoover Dam, after flowing through the Grand Canyon.