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A. Monitoring site No. 13 B. Special study site No. 15 C. Monitoring site No. 6 D. Monitoring site No. 7 E. Monitoring site No. 8 F. Monitoring site No. 9 G. Monitoring site No. 10 H. Monitoring site No. 11 I. Monitoring site No. 12 J. Special study site No. 14 The projected completion date for sites No. 6 through 15 is December 31, 1993. STUDY AREA The, study area is located within the Grand Canyon National Park, Glen Canyon National Recreation Area, and Lake Mead National Recreation Area. Limited funds and time constraints prevented the development of a GIS data base for the entire Colorado River corridor from Glen Canyon Dam to Lake Mead. A GCES/GIS work group, which includes Federal agencies, a State agency, Native Americans, and other groups, was formed to identify and select monitoring sites and provide input into the data base development. The GCES/GIS work group selected long-term monitoring sites that represented the ecological diversity in the Grand Canyon as well as areas where special studies or critical resources were located. The work group selected thirteen sites that comprise a total distance of 63 river miles throughout the canyon and encompass the river corridor from the top of the OHWZ (Old High Water Zone) river-right to the top of the OHWZ river-left. Special study sites which require monitoring such as unique or endangered cultural or natural resource components have been and will be added to the data base as appropriate. The length of the monitoring sites ranges from 2 to 12 river miles; the average monitoring site is 5 river miles long. In the future, if funds are available, the areas between the monitoring sites will be added to the data base. Because the Colorado River is a dynamic feature, the smaller scale USGS 7.5-minute DEM (digital elevation models) will be used in the interim as the linkage between monitoring sites. A location map of the monitoring and special study sites may be found on figure 1 as a foldout at the back of this report. METHODS Several technologies were involved in the development of the large scale topographic base map products to be used in the GCES/GIS mapping effort. A horizontal and vertical control network was developed throughout each monitoring site by a combination of GPS (Global Positioning System) and conventional survey methods. Aerial photography was taken to 3