 Historically, theories about migration into the Americas have centered on migration from Beringia through the interior of North America.The discovery of artifacts in association with Pleistocene faunal remains near Clovis, New Mexico in the early 1930s required extension of the timeframe for the settlement of North America to the period during which glaciers were still extensive.That led to the hypothesis of a migration route between the Laurentide and Cordilleran ice sheets to explain the early settlement.