<P> The territories of Puerto Rico and the U.S. Virgin Islands encompass a number of tropical isles in the northeastern Caribbean Sea . In the Pacific Ocean the territories of Guam and the Northern Mariana Islands occupy the limestone and volcanic isles of the Mariana archipelago, and American Samoa (the only populated US territory in the southern hemisphere) encompasses volcanic peaks and coral atolls in the eastern part of the Samoan Islands chain . </P> <P> The geography of the United States varies across their immense area . Within the continental U.S., eight distinct physiographic divisions exist, though each is composed of several smaller physiographic subdivisions . These major divisions are: </P> <Ul> <Li> Laurentian Upland - part of the Canadian Shield that extends into the northern United States Great Lakes area . </Li> <Li> Atlantic Plain - the coastal regions of the eastern and southern parts includes the continental shelf, the Atlantic Coast and the Gulf Coast . </Li> <Li> Appalachian Highlands - lying on the eastern side of the United States, it includes the Appalachian Mountains, the Watchung Mountains, the Adirondacks and New England province originally containing the Great Eastern Forest, a stretch of mixed temperature and subtropical montane forests, some of which are rainforests . </Li> <Li> Interior Plains - part of the interior continental United States, it includes the Great Plains, as well as a number of highland and mountainous regions, like the Black Hills, dense cave systems, painted hills and badland features . </Li> <Li> Interior Highlands - also part of the interior continental United States, this division includes the Ozark Plateau, the Ouachita mountains, and other smaller mountain systems . This region is located largely in the warm temperate / subtropical moist and dry forest biomes . </Li> <Li> Rocky Mountain System - one branch of the Cordilleran system lying far inland in the western states . </Li> <Li> Intermontane Plateaus - also divided into the Columbia Plateau, the Colorado Plateau and the Basin and Range Province, it is a system of plateaus, basins, ranges and gorges between the Rocky and Pacific Mountain Systems . It is the setting for the Grand Canyon, the Great Basin and Death Valley . </Li> <Li> Pacific Mountain System - the coastal mountain ranges and features in the west coast of the United States . </Li> </Ul> <Li> Laurentian Upland - part of the Canadian Shield that extends into the northern United States Great Lakes area . </Li>

What geographic features do canada and the usa share