The coastal route hypothesis, which proposes that people followed the Pacific coast southward from Beringia before the ice-free corridor was open, would be consistent with people appearing in Oregon and other western locations early in the American settlement.

The ice-free corridor hypothesis, which proposes that people moved through a gap between the Laurentide and Cordilleran ice sheets, would be more consistent with interior sites appearing early.

The timing of the ice-free corridor’s ecological viability — its ability to support the plants and animals that a human population moving through it would need — is a key constraint on the corridor hypothesis.

Geological and paleoecological evidence suggests that the corridor may not have been ecologically viable until approximately 14,000 to 15,000 years ago, which is roughly contemporaneous with or after the earliest secure pre-Clovis dates from sites like Paisley.