The San Juan River is an important source of water for agriculture and domestic use, is home to several endangered fish species, is a valued whitewater recreation area, and supports valued riparian habitat. This major tributary of the Colorado River drains 60,000 km2 (23,000 m²) of the Four Corners Region upstream from Mexican Hat, Utah, and has its headwaters in the San Juan Mountains of southwestern Colorado. The river cuts a course westward through northern New Mexico and southern Utah until it enters Lake Powell reservoir. The river was unregulated before June 28,1962, when Navajo Dam was completed; the dam's floodcontrol operations reduce peak discharges downstream. Before flow regulation, a very large flood occurred on the San Juan River on October 6, 1911, causing severe damage; however, the discharge for this flood has only been roughly estimated. Photographs of the river corridor from the 19th and early 20th centuries show a wide floodplain with sparse riparian vegetation, and repeat photographs show a large increase in both native and non-native vegetation. The purpose of this poster is to evaluate whether the 1911 flood, or other floods in the late 19th and early 20th century, explain the lack of riparian vegetation along this river, and whether flood control by Navajo Reservoir has resulted in an influx of riparian vegetation and channel narrowing.
