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reach (Schmidt and Graf, 1990). The segregation of monitoring and special study sites by geomorphic reach appear in appendix A. Second-level sub-directories of the 13 long-term monitoring and 4 special study sites reside within each appropriate geomorphic reach. Third-level sub-sub-directories representing data themes are located within each of the monitoring site directories. Within each theme, ARCANFO coverages represent the data sets developed by the contributors. An example of the data base structure is described on figure 7. GCES BASIN WIDE REACH2 REACH3 REACH4 REACH5 I I RIVER MILES I DATING I REFERENCES CLIMATE HYDSITES ELEVATION REACH6 REACH? ETC. SITE3 SITE4 TOPOGRAPHY I SOILS I HABITATS I FAUNA I RECREATION I MANMADE LEGEND GEOLOGY HYDROLOGY VEGETATION ARCHEOLOGY REFERENCEPTS TEMP Figure 7. - Tree diagram of data base structure. The GCES/GIS data base is designed as a multi-level structure which includes data that range from general to specific. Three tiers of accuracy are available within the multi-level structure, and each tier is determined by either the scale of the base map or methodology used in the development of the original data set. The first tier consists of data referenced to a 1:24,000 quad sheet and, at best, will have the National Map Accuracy Standard of 40 ft in the horizontal and half a contour interval in the vertical. The second tier of data is photo referenced and transferred to the 1:2,400 orthophoto grid base map developed for this project. The methodology used to create the 1:2,400 level can produce a digital product with a horizontal accuracy of 2.0 m and a vertical accuracy of 1.0 m. The second tier of data is being used to develop the digital long-term base products for the monitoring and special study sites. The third tier of data is survey referenced data. This data collection methodology can produce digital data with centimeter-level accuracy. The accuracy of contributed data depends on the methodology used in the collection of the original data set. THE CONSOLIDATION OF INFORMATION INTO THE GCES/GIS The Remote Sensing and Geographic Information Group in Denver developed the digital base map products for the long-term monitoring sites, as well as the protocols and methodologies to integrate the research data. Using the 1990 CIR photography, GIS coverages of geological, hydrological, and biological data for all monitoring sites were generated. Only the topographic and orthophoto products were generated for the special study sites. 8