From there it flows west through the Navajo Nation, turning northwest near Shiprock and its namesake monolith, crossing very briefly back into southwest Colorado (within half a mile (0.8 km) of the Four Corners quadripoint) before entering southeastern Utah. West of Bluff, Utah the river slices through the Comb Ridge and enters a series of rugged winding canyons, often over in depth. The lower of the San Juan River, in a remote portion of the Glen Canyon National Recreation Area, are flooded by Lake Powell, which is formed by Glen Canyon Dam on the Colorado River. The San Juan joins the Colorado in San Juan County, Utah at a point about to the north of Navajo Mountain and northeast of Page, Arizona.