Although events of the last 9,000 or so years didn’t create the large spectacular features of the landscape, this period is nonetheless interesting because it witnessed the birth of all existing park glaciers and the return of the trees composing the present-day forests. As soon as the glaciers began to shrink trees undoubtedly started to reclothe the newly exposed surfaces. New varieties came from areas which had not been glaciated. From the Pacific coast came grand fir, Douglas fir, larch, hemlock, white pine and others. From the east came another group including aspen, paper birch, hawthorn and maple. The native trees driven out by the ice also returned to again become important elements of the flora. These are Engelmann spruce, alpine fir, and lodgepole pine. A few species, among which are the alpine willows, driven southward from the far north during the Pleistocene period still persist at high altitudes but they are always ready to move down into the valleys if the climate should again become cool. Of course, continued warming would cause them to disappear. After the large Pleistocene streams of ice disappeared there followed a period of about 5,000 years during which the climate was somewhat warmer and drier than at present, conditions under which even very small glaciers could not have survived. Then about 4,000 years ago the advent of the cooler climate brought about the origin of the present glaciers. During the period of their existence they have fluctuated in size, probably attaining maximum dimensions around the middle of the last century. Since then they have been steadily shrinking, a sure indication that the climate is becoming milder, as it has so many times in the past. [Illustration: MOUNT JACKSON, VISIBLE FROM GOING-TO-THE-SUN HIGHWAY, IS COMPOSED OF STEEPLY TILTED STRATA OF THE SIYEH FORMATION. JACKSON GLACIER TO THE LEFT OF THE MOUNTAIN LIES ON THE SURFACES OF SEVERAL OF THESE STRATA. (DYSON PHOTO)] Surrounding all these small glaciers are recent moraines composed of rock debris eroded from the basins in which glaciers lie. These moraines thus represent the amount of material removed, and then deposited, within the last 4,000 years. They are particularly striking at Grinnell and Sperry Glaciers and at the site of the former Clements Glacier near Logan Pass. [Illustration: MORAINE NEAR GRINNELL GLACIER IS 120 FEET HIGH. (DYSON PHOTO)]