The Olympic-Wallowa lineament (OWL) – first reported by cartographer Erwin Raisz in 1945 on a relief map of the continental United States – is a physiographic feature of unknown origin in the state of Washington (northwestern U.S.) running approximately from the town of Port Angeles, on the Olympic Peninsula to the Wallowa Mountains of eastern Oregon. Location Raisz located the OWL particularly from Cape Flattery (the northwest corner of the Olympic Peninsula) and along the north shore of Lake Crescent, thence the Little River (south of Port Angeles), Liberty Bay (Poulsbo), Elliott Bay (setting the orientation of the streets in downtown Seattle), the north shore of Mercer Island, the Cedar River (Chester Morse Reservoir), Stampede Pass (Cascade crest), the south side of the Kittitas Valley (I-90), Manastash Ridge, the Wallula Gap (on the Columbia River where it approaches the Oregon state line), and then the South Fork of the Walla Walla River into the northeastern corner of Oregon. After crossing the Blue Mountains Riasz associated the OWL with a dramatic scarp on the north side of the Wallowa Mountains. Riasz observed that the OWL tends to have basins on the north side (Seattle Basin, Kittitas Valley, Pasco Basin, Walla Walla Basin) and mountains on the southern side (the Olympics, Manastash and Umtanum ridges, Rattlesnake Mountain, the Horseheaven Hills, the Wallowa Mountains), and noted parallel alignments at various points, generally about four miles north or south of the main line. The alignment of these particular features is somewhat irregular; modern maps with much more detail show a broad zone of more regular alignments. Subsequent geological investigations have suggested various refinements and adjustments. Introduction to a puzzle Most geological features are initially identified or characterized from a local expression of that feature. The OWL was first identified as a perceptual effect, a pattern perceived by the human visual system in a broad field of many seemingly random elements. But is it real? Or just an optical illusion, such as the Kanizsa triangle (see image), where we "see" a triangle that does not really exist? Raisz considered whether the OWL might be just a chance alignment of random elements, and geologists since have not been able to find any common unitary feature, nor identify any connection between the various local elements. called it a "fictional structural element". Yet it has been found to coincide with many faults and fault zones, and to delineate