Geology of the Eastern Klamath Mountains – May 9

The eastern Klamath Mountains flank I-5 between Yreka and Redding. This rugged upland is the oldest of nine distinct “terranes” that were added to the western margin of North America when thickened pieces of crust collided with ancient subduction zones and became sutured to the continent. Rocks exposed in the Eastern Klamath terrane record more than 300 million years of Earth’s history, from a time before animals had hard parts until the days of the great marine reptiles that prowled the Mesozoic seas. Since being added to North America, the Eastern Klamath terrane has been eroded, uplifted, and eroded again. During the past 5 million years glaciers and streams have carved the steep canyons that now dissect the region and make it so susceptible to landslides and flooding. Its tortured geologic past has also produced a wealth of gold and other mineral deposits whose extraction, sadly, has left a legacy of environmental damage.