COMBINING MAPPING AND DIGITAL ELEVATION DATA TO CHARACTERIZE STRUCTURE IN THE UPPER CROOKED RIVER BASIN, OREGON

Mapping in the Upper Crooked River region of Central Oregon reveals two significant deformational episodes. The broad-wavelength deformation poses a challenge for measurement in the field, so strikes and dips on gently-dipping geologic units were generated by a series of three-point problems using elevation data acquired from Google Earth and local LiDAR. The three-point generated strikes and dips provide consistent dip angles with errors of tenths of degrees. These strikes and dips are combined with six years of Field Camp mapping compiled to provide a summary map and cross-sections of the area. This mapping reveals a northeast-trending set of anticlines and synclines that fold all rocks up to at least 3 Ma. Rocks in these units include the classic Clarno, John Day, and Mascall Formations, Columbia River Flood Basalts (CRFB), the Rattlesnake and Divine Canyon Ash Flow Tuffs, and interbedded and overlaying local volcanics, fluvial and lacustrine deposits. Most of the fold growth occurred immediately after the time of local CRFB eruption; however, it appears that the folds had been growing slowly prior to, and continued after CRFB time. A younger, diverse set of generally northeast-striking faults (ranging from north to east) offset these folds and include the currently active east-west Paulina Fault, the largest fault in the area. LiDAR along the Paulina Fault shows south-side up, reverse slip scarps consistent with larger reverse separations in Miocene to Pliocene units. The distribution and separation of earlier folds across the Paulina Fault suggests a possible boundary in the earlier deformational event or a current additional left-lateral component of slip. However, the generally flat units and multiple broad wavelength folds make it difficult to precisely determine the lateral slip of the fault. Our approach of combining mapping and digital elevation-determined strikes and dips proves vital in characterizing deformation events that are too subtle to measure in the field.