The Olympic-Wallowa Lineament: Road Log & Backcountry Geology

In 1945, Erwin Raisz identifed a topographic feature which was oriented diagonally across the State of Washington from Port Angeles to the Oregon Wallowa Mountains. The controversy on how the Olympic Wallowa Lineament (OWL) formed remains a mystery. The State of Washington compiled geologic maps for different regions of the state including the Olympic Peninsula, Cascade Range, Yakima Fold and Thrust Belt, and the Columbia Basin. These regions belong to the OWL linear trend. Each region is characterized by different structural features along the OWL. For instance, the Olympic Peninsula from Neah Bay to Quilcene belong to an imbricated thrust fault zone where compression was directed to the southwest from the northeast direction. This zone comprises the OWL in the peninsula. The Cascade Range zone from Puget Sound to south of Easton marks the OWL with strike slip, oblique slip, and normal faults rather than thrust faults of the peninsular region. Strike slip and oblique slip faults take up stresses from both compressional and extensional forces whereas normal faults take up extensional forces. The Yakima Fold and Thrust Belt along with the central Columbia Basin return the OWL back to thrust fault compressive regimes.Rotational theories were proposed for explaining the stresses responsible for OWL development. In some instances, rotational evidence exists in the western Cascade foothills in western Lewis County where strike slip faulting and an associated shear zone were mapped. The orientation of the thrust fault systems in the Olympic Peninsula and Yakima Fold Belt-Columbia Basin suggest compression occurred from northeast to southwest which may support rotation to some degree. Beyond this evidence, the issue still remains murky at best. This book attempts to characterize the different segments of the OWL.Chapter 1 begins with a description of the OWL and the controversy behind deciphering its origin. Chapter 2 presents the OWL geologic setting and stratigraphic descriptions of the Olympic Peninsula ending with road logs of the OWL portion. Chapter 3 presents the Cascade Range segment of the central and eastern portions of the range with both road logs and back country geologic evidence of the OWL. Chapter 4 focuses on the Yakima Fold and Thrust Belt segment describing road log geologic evidence of the OWL. Chapter 5 presents more recent work completed in the central Columbia Basin segment of the OWL. Chapter 6 presents a summary of geologic observations completed for all four segments presented earlier in the text. Read more