As a linguistic medium, oral tradition conveys rich and specific detail about past events but is also subject to alteration in the course of transmission between generations. As a source for indigenous history, spoken heritage is characteristically specific in geographic attribution and thus definitive of cultural landscapes, but it is temporally under-defined because it is unconstrained by calendrical dates. We consider these qualities in relation to Tlingit oral accounts that refer to Xak-wnoowú, an 850-year-old fort in the Glacier Bay region of southeastern Alaska. The site is narratively linked to the origins of Tlingit warfare and of the Kaagwaantaan clan, and remains a landmark of historical consciousness for contemporary descendants. We apply archaeological and geological evidence to date and verify key oral narratives, finding substantial convergence with scientific data and a complementarity of perspective that potentiates fuller understandings of both Tlingit history and environmental change during the Little Ice Age. We conclude that the historicity of oral tradition—a topic of wide current debate—is clearly demonstrated at Xakwnoowú, although instances of chronological compression are revealed by the analysis.