Strata and fossils assigned to the middle-Wisconsinan interstadial on the Northern Plains within in the basins of the Missouri and Saskatchewan Rivers reflect regional conditions for the time interval immediately before the Last Glacial Maximum (LGM). This report provides AMS collagen ages and a description of mammoth remains recovered near Box Creek, Montana, and places these data within the regional context of other 14C ages, and vertebrate remains for the non-glacial interval between the Illinoian and Late-Wisconsinan glaciations.