Alluvial Chronostratigraphy and Soil Formation at a Terminal Pleistocene Mastodon Locality in Central Arizona, USA

There are few mastodon sites in the western United States with good chronostratigraphic contexts. The M&M Mastodon locality in central Arizona contained the remains of a single individual that were excavated in the 1990s; no human artifacts were found. Although six 14C ages from the locality have been published, details on the stratigraphic context of the mastodon remains have not. Here we provide details on alluvial stratigraphy and soils that include eight previously unpublished 14C ages. An averaging of three charcoal AMS 14C dates from paleochannel deposits containing and directly overlying the mastodon yields a median age of 12,900 cal yr BP. The M&M Mastodon was therefore coeval with Clovis and the Bølling-Allerød/Younger Dryas transition. This and the Billings Mastodon in southeastern Arizona are the latest dated Mammut remains in the North American Southwest and provide baseline data for modeling human versus climatic factors in terminal Pleistocene megafaunal extinctions.