Take up, first, the contour of the open type. If the map shows a stream running down the inside of the contour, there is no difficulty in saying at once that the ground feature is a valley; for instance, V, V, V, and the valley of Corral Creek on the map. But if there is no stream line, does the contour bend show a valley or a ridge?
First of all, there is a radical difference between the bend of a contour round the head of a valley and its bend round the nose of a ridge,
Compare on the map the valleys V and the ridges R. The bend of the contour round the head of the valley is much sharper than the bend of the contour round the nose of the ridge. This is a general truth, not only in regard to maps, but also in regard to ground forms. Study any piece of open ground and note how much wider are the ridges than the valleys. Where you find a "hog back" or "devil's backbone," you have an exception to the rule, but the exceptions are not frequent enough to worry over.
To tell whether a given point is on a ridge or in a valley, start from the nearest stream shown on the map and work across the map to the undetermined point, keeping in mind that in a real trip across the country you start from the stream, go up the hill to the top of a ridge, down the other side of the hill to a water-course, then up a hill to the top of a ridge, down again, up again, etc. That is all traveling is--valley, hill, valley, hill, valley, etc., though you wander till the crack o' doom. And so your map travels must go--valley, hill, valley, hill--till you run off the map or come back to the starting point.
On the map, follow the R-V line, V indicating valley and R ridge or hill. Note first the difference in sharpness in the contour bends; also how the valley contours point to the highland and the ridge contours to the lowland.
The contours go thus:
The streams flow down the valleys, and the sharp angle of the contour points always up stream. Note also how the junction of a stream and its tributary usually makes an angle that points down stream.
"Which way does this stream run?"
Water flows down hill. If you are in the bed of a stream, contours representing higher ground must be to your right and to your left. Get the elevations of these contours. Generally the nearest contour to the bank of the stream will cross the stream and there will be an angle or sharp turn in the contour at this crossing. If the point of the angle or sharp turn is toward you, you are going downstream; if away from you, you are going upstream.