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).
[Illustration: FIG. 42--A glaciated volcanic Cone: Mt. Shasta,
California, 14,162 feet high, as seen by an airplane observer from the
northeast, showing Hotlum Glacier in the foreground and Wintun Glacier
at the extreme left. The monadnock which separates the two main lobes of
Hotlum Glacier appears as the dark-colored mass of rock in the midst of
the ice. To be noted are the many indications of movement in the
glaciers shown by curved lines, eddies, and crevasses, and the glacial
streams flowing away from the ends of the glaciers. The long lobe at the
left center shows the formation of both lateral and recessional as well
as terminal moraines.]
[Illustration: FIG. 43--A glacial gorge on the northeastern face of Mt.
Shasta, California, below Hotlum Glacier (see Fig. 42), the lower end of
which is to be seen in the upper part of the photograph. At the left are
two ridges, one the edge of a sheet of flow lava, the other, in part at
least, a lateral moraine. In the center, at the bottom of the gorge,
between the two white lines which represent glacial streams, is a system
of concentric ridges which are probably recessional moraines. At the
right is the western slope of the gorge. (This figure is the lower
overlapping continuation of Fig. 42.)]
[Illustration: FIG. 44--Yosemite Valley, California, a typical
ice-shaped gorge, showing at the left the granite face of El Capitan,
about 3,000 feet above the bottom of the famous gorge, and, at the
right, the pinnacle of Sentinel Rock and the well-known form of Half
Dome. At the sky line in the center of the picture is Clouds Rest, and
well down in the gorge Washington Column and the Royal Arches can be
distinguished.]
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.
[Illustration: FIG. 45--Map of the Yosemite Valley, showing the area
included within the angle of vision of Fig. 44. The map, a reduced
section from the Yosemite and Mt. Lyell, Cal., topographic sheets,
1:125,000, published by the U. S. Geological Survey, is oriented for
direct comparison with the photograph. Scale, 1:167,000.]
[Illustration: FIG. 46--Mountains of volcanic origin: Cinder Cone with,
in the distance at the right, Lassen Peak in the northern Sierra Nevada,
California, as seen from an airplane over Lake Bidwell. Beyond the lake
appears the rough surface of lava poured out as molten rock less than
two hundred years ago (see _U. S. Geol. Survey Bull. 79_, 1891).
Surrounding the cone is a light-colored ash field, sparsely forested at
the right, which was formed about two hundred years ago. The mountain in
the middle of the photograph having a smooth surface is Cinder Cone,
rising 640 feet above the general level of the ash field and consisting
of fragments of lava--the so-called ash and cinders--blown from the
crater at times of eruption.]
[Illustration: FIG. 47--Map of the region between Cinder Cone and Lassen
Peak in the northern Sierra Nevada, California, showing the area
included within the angle of vision of Fig. 46. The map, a reduced
section from the Lassen Peak, Cal., topographic sheet, 1:250,000,
published by the U. S. Geological Survey, is oriented for direct
comparison with the photograph. Scale, 1:307,000.]
[Illustration: FIG. 48--The top of Cinder Cone, looking from an airplane
down into the crater, showing a large saucer-shaped crater 750 feet
across, with a deeper crater formed at the time of a later volcanic
explosion, which looks like a cup in the middle of the saucer and
extends to a depth of 240 feet below the outer rim. On the barren cinder
slopes at the right is the pathway by which the crater can be reached.]
[Illustration: FIG. 49--Mountain, valley, and plain in the Simi Hills
about 15 miles northwest of Santa Monica, Cal. (see Calabasas, Cal.,
topographic sheet), showing, in the right center of the picture,
headward erosion from two parallel valleys, in strong contrast with the
gently rounded, slightly dissected part of the mountain (left center)
into which the streams have not yet eaten their way. Farther up the
mountain is more maturely dissected and the divides are narrow and
steep. On its top the mountain shows little effect of stream erosion
(right). Strongly cut gorges and arroyos appear where the streams enter
the plain (left). Probably north is at the bottom of the photograph.
Scale, probably about 1:20,000.]
[Illustration: FIG. 50--A maturely dissected highland: Santa Monica
Mountains north of Santa Monica, Cal., as photographed from a height of
nearly 10,000 feet at a midday in January, 1919. The light-colored
irregular line at the left is Sepulveda Canyon; and the similar line at
the right, Stone Canyon (for location, see Fig. 51). These mountains
rise nearly 1,600 feet above sea level and about 700 feet above the
bottom of the canyons.
To obtain the proper impression of ridges and valleys the figure should
be reversed. Such photographs as this of the actual ground can hardly be
distinguished from photographs of good relief models; they strikingly
confirm the correctness of this and similar methods of representing
relief on maps, developed intuitively, as it were, such as the Swiss
school of hill shading. Scale, about 1:17,000.]
[Illustration: FIG. 51--Map of the region between the center of Los
Angeles and Santa Monica, Cal., showing the location of the area covered
in Fig. 50 (the double-ruled rectangle in the upper left corner).
Reduced from the Santa Monica, Cal., sheet, 1:62,500, of the
“Progressive Military Map” of the United States being published by the
Corps of Engineers, U.S.A. This sheet, which is the equivalent of the
Santa Monica topographic sheet surveyed in 1893 and published by the
U.S. Geological Survey, was revised in 1920 by airplane photography. A
comparison of the 1893 and 1920 editions brings out strikingly the rapid
urban development in this region. Scale, 1:123,000.]
[Illustration: FIG. 52--A young mountain gorge showing an erosional
hollow developing headward into the less deeply eroded highlands: San
Joaquin Hills, a coastal range in Southern California about 45 miles
southeast of Los Angeles, near the mouth of Aliso Creek. North is at the
left (see Corona, Cal., topographic sheet). Scale, probably about
1:10,000.]