The report is a compilation of geologic field observations and supporting laboratory data obtained during a study of the eastern slope of the High Cascade Range of Oregon, north of Broken Top volcano. General geologic relationships are summarized, then followed by lithologic descriptions, petrographic characteristics, and stratigraphic information, cross-indexed to tables of chemical analyses of pertinent rock units. The 7.5-minute N.W. Broken Top quadrange is bounded by 44/sup 0/07'30'' and 44/sup 0/15'00'' north latitude and by 121/sup 0/37'30'' and 121/sup 0/45'00'' west longitude, 6 km east of North and Middle Sister volcanoes and 35 km northwest of Bend. The quadrangle is covered by glacial till and calc-alkaline lavas, most of which originated on the adjacent slopes of the High Cascades. Basalt, basaltic andesite, andesite, and rhyodacite are represented in a variety of forms including lava flows, volcanic domes, cinder cones, and a welded ash-flow tuff.