Geologic History
Castle Crags State Park is within the Klamath Mountains geomorphic province. The eastern Klamath Mountains are built from the oldest rock in the range with the newest to the west. This is due to the continued accretions of oceanic crust added on to the western edge of North American continent. Rocks surrounding Castle Crags are mostly of the Ordovician-aged (443–490 million year old) Trinity ultramafic sheet.