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Lake Powell was formed by the Glen Canyon Dam, built at Page Arizona in 1963; it is just upriver from the Grand Canyon. Although a portion of the Lake is in Arizona, most of it is in Utah.
It is the second largest man-made lake in the US, almost 200 miles long (322km) with a coastline of nearly 2000 miles (3219km). Ninety-six major side canyons twist into the main channel of the Lake; some are 15-20 miles long (24-32km).

The dominant formation is Navajo sandstone, made of ancient sand dunes hardened into rock by pressure from deposits above them. The deposits eventually wore away and exposed the sandstone, which has been sculptured by water, wind, and time into the current formations. The brilliant red, pink, and brown canyon walls can rise hundreds of feet straight up.

Rainbow Bridge, the largest natural bridge in the world, is located in one of the side canyons. It is 290ft (88m) high, spans 275ft (83m) across, and is 42ft (13m) thick at the top of the arch. It was formed mainly by the action of water on the relatively soft sandstone. Water in contact with the sandstone dissolves the calcium carbonate (limestone) that cements the grains of sand. Water freezing and expanding in cracks breaks away entire slabs of rock. Over millions of years, a great variety of sculptures were created. Iron oxide and manganese colored the rocks various shades of pink, red, and brown.