An allostratigraphic unit, the Wyoming Valley formation, is proposed for the alluvial deposits which underlie the first terrace in the North Branch of the Susquehanna River valley. The lower bounding surface is a contact with outwash or ice-contact stratified drift at the base of the alluvial terrace. Four members are distinguished within the Wyoming Valley formation on the basis of buried soils which formed on former terrace surfaces. The members are traced through 23 stratigraphic sections in the 250 km study area on the basis of field observations, thin section photomicrographs, and laboratory analyses of grain size, soil chemistry, clay mineralogy, and magnetic susceptibility. A total of 139 radiocarbon dates constrain the age of bounding surfaces within the allostratigraphic framework. Eighty-nine of the radiocarbon dates are for samples of charred wood or nutshell from prehistoric pit features, while fifteen are for samples from geologic contexts beneath or spatially separated from any of the cultural occupations. The bounding discontinuities of the Wyoming Valley alloformation are argued to result from environmental changes which are evident in independent records from the surrounding region.