The Rockies are a masterpiece of erosion. When forces below the surface began to push them high in air, their granite cores were covered thousands of feet deep with the sediments of the great sea of whose bottom once they were a part. The higher they rose the more insistently frosts and rains concentrated upon their uplifting summits; in time all sedimentary rocks were washed away, and the granite beneath exposed.
Then the frosts and rains, and later the glaciers, attacked the granite, and carved it into the jagged forms of today. The glaciers moulded the gorges which the streams had cut. The glaciers have passed, but still the work goes on. Slowly the mountains rise, and slowly, but not so slowly, the frosts chisel and the rains carry away. If conditions remain as now, history will again repeat itself, and the gorgeous peaks of to-day will decline, a million years or more from now, into the low rounded summits of our eastern Appalachians, and later into the flat, soil-hidden granites of Canada.
These processes may be seen in practical example. Ascend the precipitous east side by the Flattop Trail, for instance, and notice particularly the broad, rolling level of the continental divide. For many miles it is nothing but a lofty, bare, undulating plain, interspersed with summits, but easy to travel except for its accumulation of immense loose boulders. This plain slopes gently toward the west, and presently breaks, as on the east, into cliffs and canyons. It is a stage in the reduction by erosion of mountains which, except for erosion, might have risen many thousands of feet higher. Geologists call it a peneplain, which means nearly-a-plain; it is from fragmentary remains of peneplains that they trace ranges long ages washed away. History may, in some dim future age, repeat still another wonder, for upon the flattened wreck of the Front Range may rise, by some earth movement, a new and even nobler range.
But what about the precipitous eastern front?
That masterpiece was begun by water, accomplished by ice, and finished by water. In the beginning, streams determined the direction of the valleys and carved these valleys deep. Then came, in very recent times, as geologists measure earth’s history, the Great Ice Age. As a result of falling temperature, the mountains became covered, except their higher summits and the continental divide, with glaciers. These came in at least two invasions, and remained many hundreds of thousands of years. When changing climate melted them away, the Rocky Mountain National Park remained not greatly different from what it is today. Frosts and rains have softened and beautified it since.
These glaciers, first forming in the beds of streams by the accumulations of snow which presently turned to ice and moved slowly down the valleys, began. at once to pluck out blocks of granite from their starting-points, and settle themselves in cirques. They plucked downward and backward, undermining their cirque walls until falling granite left precipices; armed with imprisoned rocks, they gouged and scraped their beds, and these processes, constantly repeated for thousands of centuries, produced the mountain forms, the giant gorges, the enormous precipices, and the rounded granite valleys of the stupendous east elevation of the Front Range.
There is a good illustration in Iceberg Lake, near the base of Trail Ridge on the Ute Trail. This precipitous well, which every visitor to Rocky Mountain should see, originally was an ice-filled hollow in the high surface of the ridge. When the Fall River Glacier moved eastward, the ice in the hollow slipped down to join it, and by that very motion became itself a glacier. Downward and backward plucking in the cirque which it presently made, and the falling of the undermined walls, produced in, say, a few hundred thousand years this striking well, upon whose lake’s surface visitors of today will find cakes of floating ice, broken from the sloping snow-field which is the old glacier’s remainder and representative of today.
The glaciers which shaped Rocky Mountain’s big canyons had enormous size and thickness. Ice streams from scores of glacial cirques joined fan-like to form the Wild Basin Glacier, which swept out through the narrow valley of St. Vrain. Four glaciers headed at Longs Peak, one west of Mount Meeker, which gave into the Wild Basin; one west of Longs Peak, which joined the combination of glaciers that hollowed Loch Vale; one upon the north, which moulded Glacier Gorge; and the small but powerful glacier which hollowed the great Chasm on the east front of Longs Peak. The Loch Vale and Glacier Gorge glaciers joined with giant ice streams as far north as Tyndall Gorge to form the Bartholf Glacier; and north of that the mighty Thompson Glacier drained the divide to the head of Forest Canyon, while the Fall River Glacier drained the Mummy Range south of Hagues Peak.
These undoubtedly were the main glacial streams of those ancient days, the agencies responsible for the gorgeous spectacle we now enjoy. The greater glaciers reached a thickness of two thousand feet; they have left records scratched high upon the granite walls.
As the glaciers moved down their valleys they carried, imprisoned in their bodies and heaped upon their backs and sides, the plunder from their wreckage of the range. This they heaped as large moraines in the broad valleys. The moraines of the Rocky Mountain National Park are unequalled, in my observation, for number, size, and story-telling ability. They are conspicuous features of the great plateau upon the east, and of the broad valley of the Grand River west of the park. Even the casual visitor of a day is stirred to curiosity by the straight, high wall of the great moraine for which Moraine Park is named, and by the high curved hill which springs from the north-eastern shoulder of Longs Peak, and encircles the eastern foot of Mount Meeker.
These and other moraines are fascinating features of any visit to Rocky Mountain National Park. The motor roads disclose them, the trails travel them. In combination with the gulfs, the shelved canyons and the scarred and serrated peaks and walls, these moraines offer the visitor a thrilling mystery story of the past, the unravelling of whose threads and the reconstruction of whose plot and climax will add zest and interest to a summer’s outing, and bring him, incidentally, in close communion with nature in a thou-sand happy moods.