This paper focuses on the potential for developing geologic maps using high-resolution aerial imagery and digital elevation data. A key component of geologic mapping discussed herein addresses the determination of geologic layer orientation using a planar approximation (also known as the three-point method). An analytical solution is presented which can be readily implemented in a spreadsheet. The path from initial data collection in a GIS to spreadsheet computation and back to GIS is outlined. The Mecca Hills in southern California serve as a test case, as there is good coverage with high-resolution aerial imagery, a variety of elevation data including...