The story of the geological events, as we have seen, is long. The landscape of today, we now realize, is transient. It is the contemporary product of processes that have been working day and night throughout geologic time. These processes will certainly go on and on, and inevitably will continue to change the landscape. Each year sees some little modification here and there. These small changes are not linked in our thinking with the vast sweep of geologic time, probably because our own lives are so very short. With some reflection we seem to catch glimpses of eternity as we examine the ancient gray cliffs and mighty peaks of Rocky Mountain National Park. THE MOUNTAINS ARE MANTLED WITH PLANTS Having seen that the present mountains are the result of past events, we should not be surprised to learn that the plant cover of the park is also dependent on what has occurred before. We are inclined to think of a plant community, such as a forest, as a permanent fixture; but it is a dynamic, never-stagnant population of individual living things, and in some ways resembles a community of people. Just as human populations ebb and flow through periods of great numerical growth and dominance, followed by decline and engulfment by invading peoples, so do vegetation types go through periods of dominance and decline. When certain conditions of climate and soil prevail, those kinds of plants best adapted to such conditions will dominate the scene. As conditions change, the flora will change. In Rocky Mountain National Park, we assume that toward the end of the ice age most of the high altitude landscape was either ice-covered or barren, like our present-day rockpiles above treeline. As the ice melted and disappeared, the bare rocks of the canyons were exposed, and lakes occupied what are now the meadows. The climate was changing, though, and the rather sparse arctic-type plantlife was superseded by another vegetation complex, except on the very tops of the mountains. The ice-age vegetation was presumably connected with that of the regions bordering the Arctic Ocean. The present tundra of the high country in the park is an island of arctic-type vegetation, surrounded on all sides by plant communities of lower latitudes. Will it be engulfed some day and replaced by surrounding plant types? If the climate continues to moderate, the answer may be “Yes.” Most of the original sparse arctic flora has already disappeared. The bare rocks were first invaded by lichens—those plant pioneers still to be seen on rocks in the park. In the thin soil formed by their life processes, other primitive plants became established. As the climate moderated and soils formed where bare rocks formerly existed, a new vegetation complex replaced the old.