Glen Canyon is a natural canyon carved by a length of the Colorado River, mostly in southeastern and south-central Utah, in the United States. Glen Canyon starts where Narrow Canyon ends, at the confluence of the Colorado River and the Dirty Devil River. A small part of the lower end of Glen Canyon extends into northern Arizona and terminates at Lee's Ferry, near the Vermilion Cliffs. Like the Grand Canyon farther downstream, Glen Canyon is part of the immense system of canyons carved by the Colorado River and its tributaries. In 1963, a reservoir, Lake Powell, was created by the construction of the Glen Canyon Dam, in the Arizona portion of Glen Canyon near Page, inundating much of Glen Canyon under water hundreds of feet in depth. Contrary to popular belief, Lake Powell was not the result of negotiations over the controversial damming of the Green River within Dinosaur National Monument at Echo Park; the Echo Park Dam proposal was abandoned due to nationwide citizen pressure on Congress to do so. The Glen Canyon Dam remains a central issue for modern environmentalist movements. Beginning in the late 1990s, the Sierra Club and other organizations renewed the call to dismantle the dam and drain Lake Powell in Lower Glen Canyon. Today, Glen Canyon and Lake Powell are managed by the U.S. Department of the Interior within Glen Canyon National Recreation Area. Before the Glen Canyon Dam Prehistoric cultural periods Studies indicate a chronology for the Lower Glen Canyon prehistory, "from pre-A.D. 1 to the 15th century and recorded history from 1776 to the present". A Late Basketmaker II Era (generally AD 50–500) is represented by several sites. Radiocarbon dates from charcoal material span the period between AD 250 and 440 (plus or minus 80 years). Basketmaker III is not found in the Lower Glen Canyon, but is documented in Navajo Canyon, a large left bank tributary of the Colorado River, within the geographical area of the Lower Glen Canyon. Basketmaker III introduced fired pottery, mostly Lino Black-on-gray and Lino Gray, and some small amounts of Lino Fugitive Red and Obelisk Gray. The Basketmaker culture is believed to have lasted later than Pueblo I. Pueblo I Era (AD 750–900) remains are found at Rock Creek in Lower Glen Canyon, and in Navajo Canyon. The pottery types are Kana-a Black-on-white, Deadmans Black-on-red, and Kana-a Gray, made from deposits found in Lizard Alcove. Pueblo