Build a plaster of Paris or clay model of land in a large, very deep pan. The model should depict various levels of land (hills, valleys, river beds, lakes, etc.), but the greatest height should not be higher than the side of the pan. After the plaster has hardened, slowly pour water into
the pan.

You will see that some hills become islands, shorelines change, and some areas are flooded. What is seen is much like the trailing edge or submerging portion of a continent.

What else is this like? Is it like a river being dammed and the water rises in the area designated as the reservoir?

Now use a drinking straw to dip out the water. What is seen is similar to the leading or emerging edge of a continent.

As an extension of this activity, you can develop a contour map of the land model. To do this, hold a ruler vertically against the bottom of the pan and pour in water until it reaches the 1/2 inch mark.

Now, with a soft pencil, mark the water level in a continuous line wherever the water touches the land. When you are finished, add another half inch of water, and mark again. Repeat until the highest part of the model is submerged.

When the water has been poured off, look straight down on the model and draw a picture of the lines just as you see them. The water levels can be marked on the lines. From your picture, you will be able to tell the heights of each hilltop, which way rivers flow, where level areas are, and which slopes are steepest.

If possible, compare your picture with geological survey maps. [Brilliant geologists call them "topo sheets," which is jargon for "topographical maps." ("TOPP-oh")]

It may be good to examine a topo sheet in the area where you plan to build a house or business structure. It would also be good to check a topo sheet before you go back-packing.