Sentinel Rock 28. View northeast of Sentinel Rock from offshore from Kerr Notch (Panorama J). Two thick flows of dacite of Sentinel Rock (unit dr; 306±5 ka here) fill a glacial valley carved in thinner flows of andesite of Kerr Notch (unit ak; 340±6 ka near here, Panorama I). Outcrop at lake level, left center, is andesite of phantom cone (unit apn; 346±20 and 403±12 ka near here). Photograph by Charles R. Bacon.