<P> Roughly 3 million years ago (Ma), the volcanic Isthmus of Panama formed between the North and South American continents creating a bridge over what was the Central American Seaway and allowing the migration of flora and fauna between the two landmasses in the Great American Interchange . Starting 2.58 Ma, the Quaternary glaciation covered much of the continent with ice, centered west of Hudson Bay, the floor of which is slowly rebounding after being depressed by the great weight of the ice . Glaciers descended the slopes of the Rocky Mountains and those of the Pacific Margin . Extensive glacial lakes, such as Glacial Lake Missoula, Bonneville, Lahontan, Agassiz, and Algonquin, formed by glacial melt water . "Remnants of them are still visible in the Great Basin and along the edge of the Canadian Shield in the form of the Great Salt Lake, the Great Lakes, and the large lakes of west central Canada ." The last glacial period of the current ice age caused a lowering of the sea level, exposing the Bering Land Bridge between Alaska and Siberia, which resulted in human migration from Asia to the Americas between 40,000 and 15,000 years ago . </P> <Ul> <Li> Great Plains: stretching from the Gulf of Mexico to the Canadian Arctic; </Li> <Li> the geologically young, mountainous west: including the Rocky Mountains, the Great Basin, California and Alaska; </Li> <Li> the raised but relatively flat plateau of the Canadian Shield in the northeast; </Li> <Li> the varied eastern region: including the Appalachian Mountains, the coastal plain of the Atlantic Seaboard, and the Florida peninsula . </Li> </Ul> <Li> Great Plains: stretching from the Gulf of Mexico to the Canadian Arctic; </Li> <Li> the geologically young, mountainous west: including the Rocky Mountains, the Great Basin, California and Alaska; </Li>

What are the different regions of north america