 Artifact horizons with non-Clovis lithic assemblages and pre-Clovis ages occur in eastern North America, although the maximum ages tend to be poorly constrained.Geological findings on the timing of the ice-free corridor also challenge the notion that Clovis and pre-Clovis human occupation of the Americas was a result of migration through that route following the Last Glacial Maximum.Pre-LGM closing of the corridor may approach 30k cal years BP and estimates of ice retreat from the corridor are in the range of 12 to 13k cal years BP.