 An alternative hypothesis for the peopling of America is coastal migration, which may have been feasible along the deglaciated (but now submerged) coastline of the Pacific Northwest from about 16,000 years ago.Pre-Last Glacial Maximum migration across Beringia into the Americas has been proposed to explain purported pre-LGM ages of archaeosites in the Americas such as Bluefish Caves and Old Crow Flats in the Yukon Territory, and Meadowcroft Rock Shelter in Pennsylvania.At the Old Crow Flats, mammoth bones have been found that are broken in distinctive ways indicating human butchery.