The Western Cascade Volcanic Series

The Pliocene and younger volcanic cones on the crest of the Cascade Range are flanked on the west by a belt of older Tertiary lavas and pyroclastic rocks named by Callaghan⁴ the Western Cascade series (see map, plate 2). Throughout this belt, the topography is mature and dendritic tributaries make their way between high, narrow-crested ridges to feed the major, westward-flowing rivers, the Klamath, Rogue, Umpqua, and Mackenzie. There is no trace here of the constructional slopes that characterize the High Cascades, for the rocks of the Western Cascades had already been folded and deeply eroded before the volcanoes of the High Cascades began to erupt.

Plate 2

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