Part 12 (1/2)

Upper Geyser Basin (near Castle Geyser) 7,300 ”

Mouth of Spring Creek 7,600 ”

Isa Lake, Continental Divide 8,300 ”

Yellowstone Lake 7,741 ”

Road at Mud Volcano 7,705 ”

Canon Hotel 7,850 ”

Junction Valley near Yancey's 6,150 ”

Divide between the Black-tail and Gardiner 6,550 ”

[AT] From profile of road system. For additional elevations, see list of names in Appendix A.

SCENERY.

The mountain scenery of the Park is not so imposing as that of Colorado and some other parts of the Rocky Mountain region; but it is more varied and beautiful. The eye is not wearied with the constant sight of vast and bare mountain cliffs, but finds relief in attractive lakes, streams, glades, parks, forests, and every combination of effects that helps to produce a beautiful landscape.

CHAPTER II.

Geology of the Park.

Nature seems, from the first, to have designed this region for a mountain park. In geological chronology it was near the close of the Cretaceous Period, that the lifting of the great mountain systems of the West into their present positions was practically finished. In the formation of these mountains, the general outline of the Yellowstone Park was already marked out, probably in much more striking features than at present. A vast rim of mountains, visible now in the Absaroka, Snowy, Gallatin, Teton, and Snake River Ranges, hemmed in the extensive area which has since become so famous. Subsequent events have greatly modified its original form, but the grand outlines at first determined are still distinctly visible.

In the Tertiary Period, which was next in order of time after the Cretaceous, changes of the greatest importance occurred, consisting princ.i.p.ally in the outpouring of enormous ma.s.ses of volcanic material.

The origin of these lava flows has been traced to a few craters, one of which was near Mt. Washburn, another in the Red Mountain Range, and a third near the sources of the Lamar River. Mt. Washburn has long been recognized as part of the rim of an ancient volcano. Both it and Mt. Sheridan, the two mountains which bore the princ.i.p.al part in working out the present features of that country, still remain the most prominent peaks from which the modern visitor can contemplate the work they have performed.

The outpourings at first consisted of andesitic lavas. They largely changed the appearance of the mountain ranges and to some extent filled up the interior basin. The flows were not continuous but were separated by long intervals of quiet, during which vegetation and the agencies of erosion were actively at work.

After the cessation of the andesitic eruptions, a quiescent period of great length ensued. Then came the period of rhyolitic flows, the centers of volcanic activity being as before Mts. Washburn and Sheridan. These flows built up the present Park plateau, and const.i.tute the great bulk of the rocks which the tourist now sees.

Following the period of rhyolitic eruptions, orographic agencies were active in producing extensive faults or displacements, which in certain localities radically changed the relative positions of the rocks.

The last exhibitions of volcanic energy were in the form of basaltic eruptions. These took place in part through ordinary volcanic craters, and in part through cracks or seams in the rocks, where they may still be seen forming extensive d.y.k.es. The basalt is of relatively limited extent, but its striking and picturesque forms wherever it appears make it more interesting to the tourist than any of the other rocks.

The great variety of superficial appearances which these volcanic rocks have a.s.sumed makes the Park one of the best laboratories in the world for their study.

The continuance of these various outpourings doubtless extended into Quaternary time. Then came the Glacial Epoch, the epoch of wide-spread ice-carving, which still further modified the surface of the country. The paths of the ancient glaciers have in several instances been made out and their transported material may readily be distinguished. One glacier flowed from the Gallatin Range eastward across Terrace Mountain, where it joined another moving westwardly from the Absaroka Range. The united streams continued down the Gardiner and Yellowstone Valleys, in which vast ma.s.ses of drift still mark their ancient route.

Glacial action and the common agents of denudation have given the Park country its present general aspect. These later modifications have indeed been extensive, and the great variety of form now seen in the valleys, canons and hills is the result of their combined action. The Yellowstone Canon is a marked example of erosion on a large scale. A direct result of its formation was the partial draining of Yellowstone Lake, which had previously existed at a much higher level than now, and spread over the entire area of the present Hayden Valley.

Since the cessation of the basaltic lava flows there seem to have been no further lava outpourings in this region. The old volcanoes have been long extinct and their craters have been modified almost beyond recognition. But evidences of the power which once worked beneath them are still abundant, although no longer on so imposing a scale. It is the hot springs and geysers still in existence which partly render this region so widely celebrated. That this thermal action originates mainly in the same source of energy which once poured out the vast fields of lava, there is no reason to doubt. Many plausible explanations are advanced to account for the existence of subterranean heat, but whatever may be its real origin it is doubtless the same for both cla.s.ses of phenomena.

The action which is now observable has continued in an ever-decreasing degree since the close of the lava period. Over vast tracts of the Park plateau, the rocks are entirely decomposed to unknown depths by the ascending superheated vapors. Some idea of the extent of this action may be obtained at the Grand Canon, which has cut its way a thousand feet downward into the decomposed volcanic rock without yet reaching its bottom. The infinite variety of chemic products resulting from this decomposition has given the Canon its wonderful coloration.

The same condition largely prevails over the Park plateau. Where now are dense forests and no superficial evidence of unusual conditions, there will frequently be found, by digging beneath the surface, the familiar proof that thermal activity once prevailed there. In constructing the tourist route from the Upper Geyser Basin to the Yellowstone Lake, where for nearly the whole distance there is a complete absence of hot springs, the evidences of former volcanic activity were found to be abundant.