A natural boundary is a natural feature such as a river or mountain range that divides an area into sections.
Mississippi river
Some examples of artificial boundaries are state borders that do not follow a river or other natural feature, such as the boundary between Oregon and California. Most city and county boundaries are also artificial.
Jamaica is a self contained island - it has no land boundaries.
Mississippi River & . . .
The Amazon The Aconcagua The Bio Bio are 3 examples, there are many many more.
Which river form the boundaries of the Great Lakes states
YES
Utah
the Mississippi river
columbia river
My understanding is that it consisted of all the land drained by the Mississippi-Missouri river complex. The exact boundaries were not at all precise.