Open-File Report O-11-12, Geologic Map of the Hawks Valley-Lone Mountain Region, Harney County, Oregon. 2011
New geologic mapping and supporting analytical work combined with previous observations and data reveal a complex interplay between regional mafic magmatism, regional fault patterns, and local silicic magma generation and evolution in the Hawks Valley-Lone Mountain area of southeastern Oregon. This portion of Oregon provides an ideal natural laboratory for field-based studies of mid- Miocene and younger extensional tectonism and magmatism due to well-developed fault patterns and near continuous volcanism since ~16.6 Ma. Our observations and data indicate that the Hawks Valley- Lone Mountain (HVLM) area is characterized by a NW-striking structural valley that cuts an ~150 km2 mid-Miocene, trachyte-trachydacite-rhyolite volcanic complex. New radiometric ages and stratigraphic relationships indicate that the bulk of HVLM volcanism occurred during a <1 m.y. window synchronous with or shortly following eruption of the Steens Basalt from fissures in the Steens-Pueblo Mountains located less than 20 km to the east. Scale, 1:24,000.
by Alicja Wypych, William K. Hart, Kaleb C. Scarberry, Kelly C. McHugh, Stephen A. Pasquale, and Paul W. Legge.