Devils Backbone 27. View northwest shows the two segments of the Devils Backbone dike that cut all four visible lava units (Panorama C): lower andesite below Llao Rock (unit all; 150ą9 ka here), andesite of Merriam Point (unit am; 131ą18 ka), andesite of the west wall (unit aww; 70ą4 ka), and andesite south of The Watchman (unit atw, the lava cliff on the caldera rim to the right of upper dike segment; 62ą7 ka here). Lava flows correlated with the Devils Backbone dike (unit ad; ca. 40-50 ka) extend as far as 11 km west of the caldera rim. Highest slope to the left of left dike segment is underlain by dacite of Munson Valley pyroclastic flow (unit dvb; ~35 ka). Photograph by Charles R. Bacon.