Pollen, plant macrofossil, chironomid, and lithological analyses of late-glacial sediment from Pine Ridge Pond all indicate that the warming following deglaciation was punctuated on two separate occasions by a return to colder climes; initially by a brief and moderate cold episode (the Killarney Oscillation), followed shortly by the Younger Dryas. The Killarney Oscillation, AMS 14C dated at between 11,290 and 10,960 yr B.P., is characterized by abrupt and simultaneous increases in Betula (birch) pollen and Betula glandulosa (dwarf birch) macrofossils and a decline in tree pollen. The Younger Dryas is distinguished by the reversion of a short-lived closed Picea (spruce) forest to a prolonged forest-tundra stage (ca. 10, 820 to 9500(?) yr B.P.), during which macrofossils of arctic/alpine plants such as Salix herbaces, Cassiope hypnoides, Armeria maritima, and Thalictrum alpinum make their sole late-glacial appearance. Chironomid-inferred summer surface-water temperatures indicate a cooling of approximately 8 and 12°C during the Killarney Oscillation and Younger Dryas, respectively, and coarse-sand analysis indicates increased erosion on the landscape during these same intervals.