Beaver Creek vent-dome complex 28. Aphyric rhyolite of Hinsdale Formation (unit Thr; 22.4 Ma): flow-layered lava overlies pyroclastic-vent cone; basal vitrophyre zone contains relict nonhydrated obsidian nodules (Apache tears) in perlitic matrix (Lipman, 1975, p. 93-97). In distance to right of image, basaltic lava flows of the Hinsdale Formation cap Handkerchief Mesa (southeastern Beaver Creek Reservoir quad). Photograph by P.W. Lipman.