Contrasting compositions of the youngest Columbia River basalt flows in Union and Wallowa Counties, northeastern Oregon

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement.

Several new chemical analyses of flows confined to a structural downwarp in northeastern Oregon indicate the first reported occurrence of Late-Yakima–type basalt in the region and the close stratigraphic association of Yakima–type and Late-Yakima–type flows, as well as andesite. The andesite is the most silicic flow rock yet found on the Columbia Plateau.