First, open and read CO_text.pdf, unless you require accessibility for the sight-impaired, in which case open the text only CO_text_508.pdf, instead. To see a few examples of some of the kinds of maps it is possible to create from the data in this report, view the illustrations (.pdf files) in Part B (in PartB-Figs). To view and use the data files in this report without the use of commercial GIS software (such as ArcView, ArcGIS, or MapInfo or any program that uses those file structures), install ArcExplorer (ae2setup.exe) on your computer. Other free and perhaps updated versions may be available from http:\\www.ESRI.com. Open ArcExplorer and open either the CO_geol.aep or CO_data.aep project file. Follow the instructions provided in ArcExplorer.pdf to view, query, and customize the "maps". To work with the data in Part A (PartA-Data), ArcView users may simply open the .apr files in the /ArcView/ directory and MapInfo users open the .wor files in the /MapInfo/ directory. Other files may be added to these projects or workspaces, and data layers may be turned off or removed. Be aware that the data in this report are all unprojected in latitude and longitude decimal degrees. In both the ArcView project (.apr) and MapInfo workspace (.wor) files, the "maps" are displayed projected in UTM NAD 27 for continental US, zone 13, but the data remain unprojected. Attempts to display these data with data acquired from other sources may require reprojecting or unprojecting the data, depending on the GIS software being used. Complete projection, scale, and source information for each spatial data file may be found in Part C (PartC-metadata). These files and data are for use on PC computers: they have not been tested on any other computer systems such as Macintosh or Unix. (Adobe Acrobat Reader is required to read the .pdf files. If it is not already on your computer, download and install the FREE Adobe Acrobat Reader from http:\\www.adobe.com or from PartB/AcroReader51_ENU_full.exe.)