Scanning electron microscope (SEM) examination of bone surfaces from the Pleasant Lake mastodon, excavated in southern Michigan, documents features indicative of butchery. These features are identified by comparison with modern bones modified by human and natural processes. We report new studies of (1) marks made by bone tools during removal of meat from and disarticulation of carcasses and (2) use wear developed on bone tools. We also apply previously developed criteria for recognizing stone tool cutmarks and stages in the burning of bone. The Pleasant Lake site, dated to between 10,395 ± 100 and 12,845 ± 165 b.p., provides compelling evidence of mastodon butchery and bone tool use. Another site, near New Hudson, Michigan, provides replication of much of this evidence. Together these sites offer new examples of patterns of bone modification and extend the geographic and temporal representation of the much discussed, but still controversial, late Pleistocene bone technology.