BUILDING THE MODERN GEOLOGIC MAP IN OREGON: A MULTIFACETED FIELD- AND TECHNOLOGY-BASED APPROACH

Geologic maps are required to solve practical problems, including deciphering Earth history and processes, evaluating resources, and preparing for hazards. Complexity of geologic problems necessitates efficiency in data collection, optimization of map production workflow, and enhancement of geologic models. Technological advances, such as the broader availability of bare earth lidar digital elevation models (DEMs), contemporary analytical software, and available digital data-collection devices markedly improve the accuracy and usability of geologic maps.

Modern, high-resolution geologic maps at the Oregon Department of Geology and Mineral Industries are built upon field data collected with an Apple Ipad and Esri Collector. Benefits are high-accuracy location acquisition, organization of data/photographs, and access to high-resolution base maps. Synchronization of Collector to ArcGIS online provides safe storage of data, that can be downloaded and added to ArcMap for subsequent analysis. Further in-depth data analysis takes advantage of lidar’s resolution of fine-scale features, related to underlying geologic units, by adapting techniques classically applied to interpret small-scale DEMs and topographic maps. 2D analysis of geologic/geomorphic features is accomplished using bare earth lidar DEMs shaded by slope. The addition of contours, derived from the DEMs, and the ability to examine tiny variations in elevation/slope provide more details. Models created in ArcGIS Model Builder are used to generate triangular irregular networks (TINs) representative of 3-point bedding solutions and to project planar stratigraphic horizons, contacts, or faults as more extensive DEMs. Full 3D visualization of lidar point clouds or DEMs with QT Modeler allows viewing topography from any direction/inclination, with the lighting direction adjusted in real time, further enhancing subtle features. Features identified in QT can be transferred to ArcMap by inspection, or digitized directly on the model surface in 3D and exported as a 3D shapefile.

Digital data collection, paired with 2D/3D lidar DEM analysis, revolutionizes geologic mapping and the resultant geologic models by revealing many features that have gone unrecognized using traditional topographic analysis or field reconnaissance alone.