CHAPTER X

MOUNTAIN FEATURES

(FIGS. 42 TO 52)

In obtaining photographic illustrations from the ground of mountains, canyons, and associated land forms, the same difficulty, but in exaggerated form, is encountered that obtains in securing an advantageous point of view for small objects. The difficulty is overcome in large measure by the use of aircraft. In an airplane the observer can rise above the obstructions which interfere with the view desired; can look an isolated mountain peak squarely in the face, as in the case of the photograph of Mt. Shasta (Fig. 42); can study the details of its ice cap (Fig. 42) and gaze downward on the lateral and recessional moraines left by the retreat of the mountain’s glaciers (Fig. 43). Few volcanic craters, occurring as they do at the top of cones, have been successfully photographed unless some higher mountain stands near-by on which a favorable viewpoint can be found. From an airplane, however, one can look into the very throat of a crater, as into that of Cinder Cone (Fig. 48), near Lassen Peak, California.

Much attention has been given to the interrelations of canyons, gorges, and mountain ridges, but these relations have hitherto been illustrated chiefly by means of maps and charts. Figures 49, 50, and 52 picture three relations more expressively than any map. To the experienced geographer a map may illustrate perfectly the action of a stream working headward into higher land; but the student to whom the conception of headward erosion is new will certainly grasp the idea more readily from the picture presented in Figure 52. No map could give so clear a conception of a maturely dissected highland as does a photograph like that of the Santa Monica Mountains (Fig. 50).

These photographs have the advantage of appealing to the mind through the sense of vision and will serve the same purpose as plaster models. Thus, in Figure 52, a variety of topographic forms are to be distinguished, including slightly dissected highlands with sharply incised gorges; maturely dissected highlands made up now of canyons and ridges; a mountain valley broadening out toward an intermontane plain; several arroyos; and many minor features.

In the interpretation of the features shown in a vertical view of a mountainous country the orientation of the photograph is of prime importance. When viewed in proper orientation, that is, as already pointed out (p. 5), with the shadows falling toward the observer, mountains and valleys appear in their correct relation. But, if the position of the picture is reversed, a mountain will look like a depression and a valley like a ridge. This reversal of the image can be tested by looking at Figures 49 or 52 from both viewpoints. However, since the vertical photographs will be compared with maps of the same area, it is thought better to place them on the page as if they were maps. In order to make them appear natural the prints can be turned in the necessary direction.