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However, there are many partial state boundaries, particularly in the Midwest, Northeast, and South, that are defined by rivers; in fact, only four mainland states (Colorado, Montana, Utah, and Wyoming) completely lack any borders defined by rivers or waterways, as well as Hawaii whose borders are the islands. Map of U.S. river/waterway state ...
The northwestern border was defined as a line running west from the northwestern point of the Lake of the Woods to the Mississippi River, but the river's source was south of that; maps universally show the line as running directly from the Lake of the Woods to the river's source, Lake Itasca. The border extending from Lake Superior towards the ...
The course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River at the city of Cairo, Illinois. Where the Ohio joins the Mississippi is the lowest elevation in the state of Illinois, at 315 feet (96 m).
The Colorado River meets the Mexico–United States border at the Northern International Boundary (NIB), where the Morelos Dam diverts nearly the entire remaining flow into the Reforma Canal and the Tijuana Aqueduct. Most of this water is used for irrigation in the Mexicali Valley, one of Mexico's most fertile agricultural regions. [7]
The Northwest Angle in Minnesota, bordering Manitoba, Ontario, and Lake of the Woods. There are several exclaves between the United States and Canada, including the entire state of Alaska (though the state can still be accessed by sea from the United States, except the small settlement of Hyder, which is only accessible by road from British Columbia).
Age of the bedrock underlying North America, from red (oldest) to blue, green, yellow (newest). Seventy percent of North America is underlain by the Laurentia craton, [5] which is exposed as the Canadian Shield in much of central and eastern Canada around the Hudson Bay, and as far south as the U.S. states of Michigan, Wisconsin, and Minnesota.
Few fossils of terrestrial life are known from the Mississippian of North America. [30] During the ensuing Pennsylvanian, the northward drift of Gondwanaland finally joined the southeastern United States to North America as Pangaea began to form. Mountain building raised the Ancestral Rockies in Colorado, Utah, and Wyoming.
The receding formation of glaciers 15,000 years ago, at the end of the last ice age, left large amounts of water in North America, which created the rivers. [22] The Mississippi River stemmed from Lake Itasca in northern Minnesota where it was only a tiny outlet stream. It worked its way 2,350 miles (3,780 km) south to the Gulf of Mexico.