Samples of live geoducks and intact dead geoduck shells were collected from sites near Tofino, on the west coast of Vancouver Island, British Columbia, in 2004, 2006, and 2008. Shells were aged by the Sclerochronology Laboratory at the Pacific Biological Station using the dendrochronological technique of cross-dating. The year of death of the dead shells was determined by using the novel technique of overlapping the synchronous growth patterns of the live and dead shells. Results indicate that most of the geoducks in the sample, regardless of age, died in 1991 and 1992. We investigated possible causes of their deaths. We conclude that the mass mortality of geoducks on the exposed west coast of Vancouver Island may be the result of wave-induced anastrophic (localized catastrophic) burial.