Adjoining the Roundtop lava on the northwest is a second thick sheet of andesite which likewise poured down a broad valley cut in glacial deposits. Accordingly, the thickest part of the flow is in the center, where the great cliffs of jointed lava descend to the lake forming the so-called Palisades. Where there is no talus, the underlying materials consist chiefly of fluvioglacial sands and gravels. Especially clear are the exposures beneath the eastern “wing” of the flow, where the downward succession is as follows: talus, 10 feet; coarse, bouldery till, 10 feet; fine glacial sands and gravel, 4 feet; coarse till with boulders up to 2 feet across, 6 feet; fine, well bedded sand with scattered boulders, 20 feet; coarse till with boulders up to 3 feet across, 5 feet; fine, well bedded sand and gravel, 12 feet; till with boulders up to 18 inches across, 5 feet. Toward Roundtop, these bedded deposits probably double or even treble in thickness and interfinger with the more massive moraines already described. Beneath the western “wing” of the Palisade flow, the underlying rocks are almost wholly hidden by talus, and where they do outcrop their nature is such that it is impossible to decide whether they are glacial in origin or represent the bouldery products of volcanic mudflows (lahars). Similarly, no certain glacial deposits have been identified beneath the dacite flow in Cleetwood Cove.
Although, as we have noted, the top of the Roundtop flow has been polished by ice and lenses of glacial till rest on it, no such signs of glaciation can be seen on the bristling top of the Palisades flow, above which lie first a thick pile of coarse lump pumice and then welded tuff. Above the tuff, however, are bouldery deposits that seem to represent glacial moraines. The Cleetwood flow is also overlain in part by lump pumice, and, along its lower margins, by welded tuff. The higher, central part of the flow, on the other hand, is overlain by bouldery detritus up to 150 feet thick. Whether this deposit is entirely morainic or the product of eruptions which hurled out occasional glacial boulders cannot be decided. Ice did, however, cover at least part of the Cleetwood flow, for in the cuts along the Rim Road the lava is overlain first by red, buff, and white lump pumice, then by glacial sands and bouldery till, and finally by the ash and pumice deposits laid down during the culminating explosions of Mount Mazama.
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