What physical features have acted as barriers to settlement in the united states and canada

The natural features includes Appalachian Mountain, Rocky Mountains, Great Plains, Interior Plains, Canadian Shield.

Physical feature refers to geological element produced by nature such as soil, slopes, lakes, flood plains, oceans, rocks, sands, mountains, valley etc

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The Canadian shield is a plateau in Canada that is filled with bare rock outcrops and very thin topsoil due to glaciation. The lowlands in this area are also not good for agriculture since they don't retain moisture and are always frozen in permafrost.  

The Appalachian mountain also acts as a physical barrier to the movement of people from east to west. In addition, due to the fact the west is on the leeward side, it is less favorable for settlement because of very little annual rainfall and drought.  

The River system in North America that stretches along Mississippi-Missouri-Jefferson Rivers  also impeded easy movement of people towards the north from the south especialy in the past before water transport became easily available and affordable to people.

answer(c) carved on a babylonian clay tablet that showed earth as a flat circular disk;