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In land forms resulting from water erosion, contours along stream channels are normally V-shaped, the V pointing upstream; shoulders and ridges are usually U-shaped, the U pointing downhill. An understanding of the main drainage system will make it easier to understand the relation of ridges and minor valleys and gullies to the main canyons and mountain systems. A contour line cannot end except on itself (or at the edge of the map). If it ends on itself, it will form a closed circuit which usually indicates a peak or ridge crest, the interior portion of the circuit being higher than any portion along its edges. Such contours may also show a depression. For that use, they are usually marked with short, right-angle lines inside the closed circuit. In desert regions, depressions may be on such a vast scale that such a method of marking is not practical. They may then be recognized by the form of the rest of the topography and a careful check to determine which contours are higher than others. |
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