Loss Creek is a river on southern Vancouver Island that flows from a point north of River Jordan, British Columbia due west to Sombrio Beach (southeast of Port Renfrew), mostly following an unusually long, straight, narrow, and steep-sided valley. This valley is the surface trace of the Leech River Fault, a major regional fault that marks the contact between the oceanic basalts of the Crescent Terrane (part of Siletzia) to the south, and the metamorphic rocks of the Pacific Rim Terrane to the north. The Leech River fault is straight because it was originally a strike-slip fault (moving horizontally), but now it is being thrusted under Vancouver Island.