[citation needed] The ice sheet covered up to 1,500,000 km2 (580,000 sq mi) at the Last Glacial Maximum[2] and probably more than that in some previous periods, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho.

[7] This rapid retreat resulted in noticeably fewer glacial landforms in the west of the Cordilleran's maximum extent compared to the south and east, though the exact mechanisms behind this disparity are unknown.

[8] Many of the southern and eastern landforms fall near the northern reaches of the American Cordillera, the mountain ranges which geologists believe to be the region from which the Cordilleran first grew, and, after its sudden retreat and ultimate collapse, where it terminated.

In particular, the collapse of the western front of the Cordilleran ice sheet has been proposed as one route through which early humans could have migrated after crossing the Beringian Land Bridge during the Last Glacial Maximum.

Some underwater features along the Pacific Northwest were exposed because of the lower sea levels, including Bowie Seamount west of Haida Gwaii which has been interpreted as an active volcanic island throughout the last ice age.

These effects are important because they have been used to explain how migrants to North America from Beringia were able to travel southward during the deglaciation process due purely to the exposure of submerged land between the mainland and numerous continental islands.