GEOLOGIC MAP OF THE CRAFT POINT QUADRANGLE, HARNEY COUNTY, OREGON, USA

The Craft Point 7.5-minute quadrangle in Harney County, Oregon, is about 30 km northeast of downtown Burns. Situated between the northeast corner of the Harney Basin and the southern flanks of the Blue Mountains, and straddling the southeastern border of the Malheur National Forest, Craft Point Quadrangle was initially mapped in the 1970s as part of a regional reconnaissance map. About 75% of the quadrangle was mapped as Tba (Miocene Basalt and Andesite), with the remaining areas mapped as Tst or Tsts (tuffaceous sedimentary rocks, Pliocene or Miocene and Pliocene, respectively), Twtp (welded tuff of Prater Creek), and Tdv (welded tuff of Devine Canyon). Our recent mapping provides a more detailed geological account, revealing Oligocene-aged dacite, early Miocene rhyolites, two cooling units of mid-Miocene Dinner Creek Tuff, late Miocene Rattlesnake Tuff, and numerous north- to northwest-trending normal faults. Geochemical compositions of basalt and basaltic andesites, previously mapped singly as Tba, were closely evaluated through compositional correlation diagrams and supervised machine learning classification. We determined that the basalt and basaltic andesites originated as either lavas of the Columbia River Basalt Group (CRBG), particularly the Picture Gorge Basalt – the oldest and longest erupting member of the CRBG, or lavas of the Strawberry Volcanics. Ar/Ar geochronology yielded an age of 16.16 Ma for one basalt sample and 15.74 Ma for one basaltic andesite sample, correlating with early CRBG activity. Co-CRB rhyolites, with one sample yielding an age between 16.60-16.20 Ma, were also mapped. Lava of the CRBG accounts for about 45% of the map area, while the rest is covered by lavas of the Strawberry Volcanics (15%), Miocene ash-flow tuffs (15%), co-CRB rhyolites (14%), surficial deposits (10%, mostly tuffaceous sediment), and Oligocene dacite (1%). This project enhances understanding of the volcanic framework of eastern Oregon, expands volume and distribution estimates for Picture Gorge Basalt and lavas of the Strawberry Volcanics, and delineates previously unrecognized faults related to the Northwest Basin and Range extension. Furthermore, this map provides a strong foundation for future research aimed at critical mineral exploration and water resource management.