The Picture Gorge Basalt Subgroup was mapped over an area of 1,600 km² in the John Day Basin in north-central Oregon. Lateral continuity of the Twickenham, Monument Mountain, and Dayville Basalts is demonstrated, and each is elevated to formation status within the Picture Gorge Basalt Subgroup of the Columbia River Basalt Group. Seventeen members are defined based on field and compositional characteristics. Sixty-one flows are identified, of which 39 belong to recognized members. The remaining 22 flows that are unassigned are of limited areal extent. Compositional data and field characteristics were used with the assistance of discriminant analysis to...