The Yellowstone plateau is a vast lava-deposit. Its material is mostly
volcanic, but its landscape--its architecture--is largely glacial. In
ages remote, this realm became the scene of volcanic activity.
Intermittent outpourings went on through long periods of time.
Volcanoes in and near the Park threw forth quantities of ashes, lava,
and cinders, which built up a plateau region three or four thousand
feet thick. Rhyolite and other forms of lava were last spread over
the region. This volcanic activity appears to have ended before the
last ice age. No eruption has occurred for centuries. The ice age
wrought vast changes in the volcanic landscape. The ice smoothed wide
areas, shaped cañons, and rounded mountain-sides, produced and spread
soil, and gave the entire region the flowing, attractive lines of
glacial landscape.
On the rim of the Yellowstone Cañon, about three miles below the
falls, an enormous glaciated granite boulder reposes upon
lava--rhyolite. It measures about twenty-four by twenty by eighteen
feet. It was transported to this resting-place from mountains more
than thirty miles away. Here we have a stone foundation laid by
volcanic fire, and upon it a stone, shaped, transported, and placed by
glacial ice.
There are about three thousand geysers, hot springs, and mud-and-water
springs in the Park; and as many other vents of steam, acid, and gas.
That the geysers have been active in this region for thousands of
years is shown in the deep deposits of silica and travertine that
overspread extensive area. During the ice age many of these deposits
were eroded and others were piled with boulders. It is plain that
steam and hot water had been at work long before the last ice age
came. During the ice period, a wild conflict probably took place
between the deep outspread ice and the insistent eruptions of steam
and hot water.
The surface of Yellowstone Lake once stood about one hundred and
eighty feet higher than it is at present. Its outlet was then through
the Snake River to the Pacific Ocean. The Continental Divide then
passed over the summit of Mount Washburn. Unwritten as yet is the
splendid geological story of this change, which may have been caused
by earthquake upheaval or by subsidence. It appears to have occurred
about the close of the last glacial epoch. Possibly ice dammed the
narrow gorge of Outlet Creek, through which the waters of the lake
formerly flowed to the Snake River. Whatever the cause, its outlet
waters changed and eroded the now famous and splendidly colored cañon
of the Yellowstone.
This is the most celebrated cañon in the Park, and its colors make it
one of the most gorgeously startling in the world. At bright noonday,
it is adorned with all the hues of the sunset sky. Its precipitous
walls are comparatively free from vegetation and are broken with
pinnacles and jagged ridges. About fifteen hundred feet below the
edge, the rushing waters of the Yellowstone River take on various
shades of blue and green between accumulations of gray foam.
Into the upper end of this cañon the river, about seventy feet wide,
makes a sheer leap of three hundred and ten feet. From the near-by
rim, this wonderful waterfall appears like an enormous, fluffy,
endless pouring of whitest snowflakes. The magnificence and wildness
of its setting combine to make it one of the most imposing waterfalls
in the world.
The paint-pots are the curiosities of the Park. They are craters, or
irregular-shaped ponds, in the earth, filled with brightly colored
mud, thick and hot, of fine texture, and in appearance resembling
kalsomine or paint freshly mixed and colored. The mud in many pots is
red or pink; that in others is lavender, blue, orange, or yellow.
Occasionally a rugged vat of this mud is found boiling away--very
suggestive of slaking lime. In other cases, plastic mud throbs and
undulates as steam-jets now and then escape through it. Here and there
this bright steamy mud opens like a full-blown lily. The paint-pots
near the Fountain Geyser, those east of the road in Gibbon Meadows,
and those close to the lake at the Thumb are the more attractive.
[Illustration: GRAND CAÑON FROM ARTIST POINT
YELLOWSTONE NATIONAL PARK _Copyright by Haynes, St. Paul_]