FANTASTIC MAPS AND WHERE TO FIND THEM: CREATING A NEW GENERATION OF GEOLOGIC MAPS FOR TEACHING STRUCTURAL ANALYSIS AND CROSS-SECTION CONSTRUCTION

Traditional methods for teaching students how to analyze structures in geologic maps and to construct cross-sections rely on paper maps with topographic contours and standard drafting tools. This approach helps students learn how to visualize structures on maps, but it does not introduce them to digital maps and, more importantly, to computer programs that incorporate elevation data for map analysis. For example, GeolMapDataExtractor (GMDE) (Allmendinger, 2019) is a versatile program that can use digital geologic maps to perform 3-point problems, calculate stratigraphic thicknesses, project contacts across topography, and construct topographic profiles. Orientation data can also be entered manually based on measurements recorded on the map. Elevation data can be entered manually from topographic contours, obtained from web-based elevation servers, or read from user-provided DEMs for offline use. Some published geologic maps are suitable for teaching purposes, but even the simplest maps may be too complex for beginning students. A suite of simple to complex synthetic geologic maps, illustrating specific geometries, can be used to bridge the gap between traditional paper map exercises and computer-based map analysis for teaching purposes. A DEM from a real region with suitable topography is imported into Trimble SketchUP (SU) where topographic contours are added. A cross-section illustrating stratigraphic contacts, folds, and faults is constructed on a vertical plane in SU and projected with the push-pull tool into the DEM. The intersection of the projected cross-section with the DEM is used to create the geologic contacts. If desired, the maps can be printed for use in traditional map exercises. The same maps can also be used in GMDE to show students how to determine the orientation of contacts, to estimate the stratigraphic thickness of map units, to project contacts across topography, and to begin cross-section construction. Because the DEMs are based on actual topography, elevations can be obtained from web-based servers or read from the DEMs for offline use. By using SU it is possible to generate a large number of geometrically consistent synthetic geologic maps of increasing complexity in a reasonable amount of time. These maps can help introduce students to some of the methods of modern structural geology.