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as well as scientists and engineers for conven- tional technical applications. Today, scientists and engineers increasingly depend on digital (computerized) base maps for their research and analyses. The USGS is working to ensure the availability of accurate digital carto- graphic data for the Nation to facilitate ground-water and hazards studies, and land- and resource-management activities. In summer 1995, the Rocky Mountain Mapping Center moved into newly renovated office space on the Denver Federal Center in Building 810. The move allowed the Center to improve service to customers by consoli- dating all Denver-based production, research, and distribution operations into a single facility. The Center is responsible for the development of cartographic and geo- graphic data and applications for the Western United States and for the dissemination and sales of published mapping information. Digital Raster Graphics Digital raster graphics (DRG; scanned topographic maps) are being produced in cooperation with several Federal, State, and local agencies for more than 1,000 of the I :24,000-scale USGS topographic maps of Colorado. DRG's in progress in the State are shown in figure 2. DRG's are used as map bases or backdrops on which other informa- tion can be overlaid so that the other informa- tion can be combined with the familiar USGS topographic map. Users now combine these products manually on mylar or paper maps; DRG's will allow users to automate processes and to increase efficiency. The DRG's can be used in many ways. The BLM can use DRG's in its Emergency Fire Suppression Program. The boundary of a fire can be mapped by collecting global positioning system points, and the outline can then be overlaid on the DRG for refer- ence to the terrain. This information helps helicopter pilots and firefighters plan their method of fighting a fire. The Colorado Divi- sion of Wildlife can use DRG's as a back- 1090 410 1070 1050 1030 3r , ._.~ Figure 2. Digitial Raster Graphics in progress. drop to overlay boundaries for its property- management program. Wildlife managers also can display point locations on the DRG to show wildlife distribution. Watershed-Modeling Systems Initiative in the San Juan River Basin Competition among users of the water resources in many Western drainage basins has increased pressure on water managers to provide relevant, near real-time assessments of water availability and use. Hydrologic and water-management models help managers develop these assessments. The purpose of this initiative is to develop, test, and imple- ment water-resource models and integrated data-management systems that are designed to help manage the water-related infrastruc- ture. This study is a collaboration between the USGS and the BOR and focuses on water-management issues in the San Juan River Basin, which is a tributary to the Colo- rado River. The Basin provides a diverse physical and hydrologic setting for testing and implementing water-resource models. Drought History and Climatic Change in Eastern Colorado Droughts have occurred in some parts of the Great Plains of eastern Colorado in nearly every decade of this century; droughts were severe in the 1930's, 1950's, and 1970's. Massive dust storms spawned by wind erosion during drought periods threaten the health, comfort, and livelihood of large segments of the population for long dis- tances downwind. During the 1930's, blow- ing dust closed highways and railroads, cut off power, and blocked the Sun. Aircraft were adversely affected by dust carried aloft. In the 1990's, this impact is more serious because of modern air traffic. USGS scientists are studying the distribu- tion and history of windblown sediment in eastern Colorado to improve understanding of the frequency and cause of droughts in the Great Plains, the geological factors that con- trol wind erosion, and the potential impact of climatic change on water supplies, soil ero- sion, and land-use practices. These studies indicate that droughts much more severe than any of the historic droughts are possible under the present climate. Effects of Acid Precipitation on Rocky Mountain Lakes and Streams To determine which Rocky Mountain lakes and streams are most at risk for acid precipitation, the USGS has determined the chemistry of the snowpack and the lakes and streams fed by snowmelt. The chemistry of the snowpack determines how acidic the snowmelt that supplies water to these aquatic systems becomes. The chemistry of the lakes and streams determines how susceptible these systems are to damage by acidic snowmelt. The most acidic snow in the Rocky Moun- tains falls in northern Colorado in and near the Mount Zirkel Wilderness Area. Because of the geology, lakes and streams of the Mount Zirkel Wilderness Area are among the most sensitive to acidic precipitation in the Rocky Mountains. Thus, in this area, the most acidic snowpack overlaps the most sensitive aquatic systems. The USGS, is working with local, State, and Federal agencies, as well as with industry and environmental groups, to determine what damage might have occurred or is likely to occur in the Wilderness Area. One of the possible effects is damage to trout and amphibian populations. Information Centers The USGS National Earthquake Informa- tion Center (NEIC) in Golden collects, pro- cesses, and distributes information about more than 20,000 seismic events each year. This information is distributed as alerts, bulle- tins, and routine catalogs to Federal and State emergency-management officials, critical- facilities operators, news media, the general public, and the earthquake-research commu- nity. These catalogs of recent and historical earthquake information are used in earthquake-hazards assessments. To fulfill its mission, the NEIC has developed and is deploying the U.S. National Seismograph Network (USNSN), which, when completed, will consist of about 60 seismograph stations nationwide. The USNSN monitors nation- wide seismicity, provides early notification of seismic events to national emergency-services personnel, maintains an archive of high-qual- ity digital data on national seismicity, and provides public information on earthquakes. The USGS's Earth Science Information Center (ESIC) is located in at the Denver Federal Center. The ESIC offers information and sales services for USGS map products and earth science publications. The ESIC can provide information about geologic, hydrologic, topographic, and land-use maps, books, and reports; aerial, satellite, and radar images and related products; earth science and map data in digital format and related applications software; and geodetic data. The ESIC can fill orders for custom products, such as aerial photographs and orthophotoquads, digital cartographic data, and geographic-names data.