Key Ideas

• The Earth’s surface has recognizable shapes: mountain ranges, plateaus, plains, valleys, basins, and deltas.
• Streams and rivers are rainfall draining off the land. Water can only run downhill, so a river sits where the low line is.
• A river’s size depends on two things: how much rain falls, and how much land drains into it.
• All the land draining into a river is its watershed. Adjacent watersheds are always separated by higher ground called a divide.
• Every river eventually reaches an ocean or a salt sea, and every piece of land on Earth belongs to some river’s watershed.

• Topography: The shape of the land surface: how high, how low, how steep, and how it is arranged.
• Range, plateau, plain: A mountain range is a long line of high ground. A plateau is high ground that is flat on top. A plain is wide, low, and flat.
• Valley and basin: A valley is low ground between higher ground. A basin is a low area with ground rising all the way around it.
• Watershed: All the land that drains into a particular stream or river.
• Divide: The higher ground separating two watersheds.
• Tributary: A smaller stream or river that flows into a larger one.

1. Two rivers get the same amount of rain, but one is much bigger. What must be true about the land around them?
2. Somebody spills something harmful on the ground fifty miles upstream from a city. Trace what happens, and say who else it eventually affects.
3. Look at where the oldest big cities in the world are. Why do so many of them sit on rivers, and why so many at the mouth of one?

• A large world map, wall space, colored yarn, tacks or tape, and printed photos or satellite images
• A satellite map you can zoom and scroll, and a notebook