Laserfiche WebLink
<br />8 <br /> <br /> <br />002458 <br /> <br />tributary debris fans, large rapids, and steep average gradients (Grams and Schmidt, <br />1999). Because debris fans exert a dominant influence on many channel attributes, these <br />reaches are typically referred to as debris fan-dominated canyons (Schmidt and Rubin, <br />1995; Grams and Schmidt, 1999). Canyons cut into less resistant formations tend to have <br />few debris fans, small rapids or riffles, and lower average gradients. These reaches are <br />often referred to as incised meanders, because the river channel typically flows in an <br />entrenched meandering valley (Harden, 1990; Grams and Schmidt, 1999). While Grand <br />Canyon is the largest debris fan-dominated canyon of the Colorado Plateau, Glen Canyon <br />was the longest canyon formed of incised meanders. <br />The Glen Canyon region includes over 200 km of the Colorado River corridor <br />plus hundreds of tributary canyons stretching from Hite, Utah downstream to Lees Ferry, <br />Arizona (Figure 1). Most of this expansive region is now flooded by Lake Powell, the <br />reservoir formed by Glen Canyon Dam. The subject of this paper is the 25-kIn of Glen <br />Canyon downstream from the dam. For the first 21 kIn downstream from the dam, <br />bedrock from river level to the tops of the canyon walls is Triassic/Jurassic Navajo <br />Sandstone, which is also the dominant formation in the flooded portions of Glen Canyon <br />upstream. Bedrock near Lees Ferry, from 21 to 25 kIn downstream from the dam, <br />includes highly erodible Triassic conglomerates, sandstones, and shales that are <br />stratigraphically below the Navajo Formation. These formations include the Kayenta, <br />Chinle, Shinarump, and Moenkopi. Several small tributaries enter Glen Canyon between <br />the dam and Lees Ferry. Although some of these tributaries have small fans at their <br />mouth, none form debris fans comparable to those that occur in Marble Canyon <br />downstream from Lees Ferry. <br />Locations in Glen Canyon are commonly referenced by river mile (RM), which <br />by convention is measured in miles upstream from Lees Ferry with a "-" sign to avoid <br />confusion with locations downstream from Lees Ferry. We use the RM convention for <br />place names that can be identified on river guides or maps that use this reference system. <br />However, we report and plot most data in the more convenient format of distance <br />