Part II. Drainage basins & divides
1. Find the Ohio River. It flows into the Mississippi at the southern tip of Illinois. Trace it in blue. Notice that it flows westward from Pennsylvania. But there is something different about its source. The Ohio is formed by two other rivers, the Allegheny and the Monongahella. They join at Pittsburgh to become the Ohio. Trace each of these rivers in blue as well. Do you see how your tree continues to grow? The Mississippi is the trunk and the Missouri and Ohio are its two biggest branches. Now trace in blue all the remaining rivers you can find feeding into the Mississippi. |
| 2. When you have finished coloring your blue rivers, you will see that most of America's middle is drained by the Mississippi. This is the Mississippi River "drainage basin." To the east and west of this basin are two mountain ranges; what are they? In 1682 Robert LaSalle explored the Mississippi and claimed its drainage basin for France. What part of America was he claiming? |
| 3. Look in Illinois above the place where the Ohio joins the Mississippi and see if you can find the Illinois River. Locate its source near the large lake northeast of Illinois. Notice it does not quite connect with the lake. What is the name of the lake? It is one of five we call the "Great Lakes." Follow the chain of these lakes eastward and notice they become the source of the "St. Lawrence River" separating Canada and America. This river feeds into what ocean? Trace the St. Lawrence River in green and color the Great Lakes green as well. |
| 4. The point where the Illinois River is closest to Lake Michigan is on a divide. This is an imaginary line that separates drainage basins. Water from north and east of this line goes into the Atlantic Ocean. Water south and west of this line enters another part of the Atlantic. What is it? |
| 5. Sometimes rivers form so close to a divide that boats and goods can be carried from one to the other. Before there were roads, this was a good way for travelers to go from one river or lake to another. We call it a portage. There are many portages between the Mississippi drainage basin and the Great Lakes. Some of these portages were made into canals. A canal is a man-made river which usually uses dams and locks to control flow of water each way. There is a very important canal on the Chicago River between the Illinois and Lake Michigan. It allows boats to pass all the way from the St. Lawrence to the Gulf of Mexico! |
| 6. Now you can trace all the other rivers flowing into the Atlantic Ocean east of the Mississippi. Use your green pen for this. See how the Appalachian Mountain chain divides your green and blue rivers. Why is this? |
| 7. Now go west of the Mississippi and find the Rio Grande River. It forms part of the boundary between America and Mexico. Trace it in green as well as the other rivers entering the Gulf of Mexico west of the Mississippi. Where is the source of the Rio Grande? |
| 8. Now you have colored most of America's rivers, but one important part remains blank. Which is it? Use a red pen and trace the rivers there. Notice the two biggest ones, the Columbia and the Colorado. One goes into the Pacific near Portland, Oregon. The other goes into the Gulf of California in the far southwest. What separates these rivers from the green and blue ones you've already traced? |
| 9. This marks another divide. It is a very special one. We call it the "Continental Divide" because it separates rivers feeding the Atlantic from those feeding the Pacific. It divides our North American continent. What do you notice about the parts of America you have now colored? (As you study America's past, you will see how these rivers and divides changed our nation.)
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