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270 Y.K. CONVERSE ET AL. Reach 3 Reach I I~ Reach 2 ~ .. Figure 2. Map of the study area showing geomorphic reaches deep corridor, whereas it is wider and shallower in regions of locally erodible lithology (Howard and Dolan, 1981). These changes are used to designate three contiguous reaches in the study area (Figure 2). Reach 1. In reach I, Tapeats Sandstone dominates the geology at the river surface where the LCR flows into the main channel (RM 61.4). Tapeats is a medium to coarse-grained sandstone (Middleton and Elliot, 1990). Layers are differentially eroded but generally resistant which causes characteristic ledges and cliffs 30-100 m above the river surface in a narrow corridor (Middleton and Elliot, 1990). Below RM 63, the geology shifts to the Dox Formation consisting of: Ochoa Point, Comanche Point, Solomon Temple and Escalante Creek in descending order. Because these underlying strata are tilted, the lower Escalante Creek member of Dox Formation is the first Dox strata encountered at river level. This cliff forming layer maintains the narrow river corridor (Hendricks and Stevenson, 1990). Reach 2. At Lava Chuar Canyon (RM 65.5), the river crosses the Palisades Fault. Here, geologic strata are displaced, and upper, more erodible members of Dox Sandstone emerge at river level. The river is shallower and the corridor widens as the river cuts into the shaley, more erodible Ochoa Point, Comanche Point and Solomon Temple members of Dox Formation (Billingsley and Elston, 1989). The channel continues as such to below Unkar Rapid (RM 73.4). Reach 3. Below Unkar Rapid, the Escalante Creek member resurfaces (Billingsley and Elston, 1989) and the river channel narrows again continuing as such through resistant Shinumo Quartzite (RM 75.4). Hakatai Shale dominates the shoreline at RM 76, about I km upstream of Hance Rapid (RM 76.5). The brief emergence of the erodible shale does not affect the channel morphology, and the corridor remains narrow through the end of the study area at Hance Rapid (RM 76.5). \ METHODS Study design This study was one component of a larger project that focused on the ecology of the humpback chub in the Colorado River through Grand Canyon (Valdez and Ryel, 1995). To address the objectives of this study, three types of data were collected at two nested spatial scales: reach and shoreline. First, we 10 1998 John Wiley & Sons. Ltd. Regul. Rivers: Res. Mgmt. 14: 267-284 (1998)