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The Shasta River Drains Two Geologic Provinces

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The Shasta River drains two mountain ranges that belong to different geologic provinces. The Cascades, a string of volcanoes, lie to the east of the river. There is little surface runoff from these mountains because most of the water percolated through lava tubes in the porous, volcanic rocks. The Klamath Range, to the west of the river, capture most of the moisture moving inland from the ocean, leaving the Shasta Valley dry. The Klamath Mountains are made of ancient rocks that were once at the bottom of the ocean, and were uplifted through plate tectonics.

Map drawn by Gary Bloomfield, from Klamath River Studies for Grades 7-8. by Diane Higgins