A RAW LOOK AT THE OWL

The Olympic-Wallowa lineament (OWL) is an alignment of geologic structures extending from the Olympic Peninsula-Puget Sound area of western Washington to the Wallowa Mountains of northeast Oregon. It trends NW to SE across Washington crossing through the Columbia Basin and forming the southern boundary of the Pasco Basin. Within the Columbia Basin, the OWL aligns with over 200 kms of folds that are part of the Yakima fold and thrust belt and includes the alignment of structures from Rattlesnake Mountain to Wallula Gap and the Wallula fault zone (WFZ) commonly referred to as the Rattlesnake-Wallula alignment (RAW). The WFZ extends from the Blue Mountains to Wallula Gap. From Wallula Gap to Rattlesnake Mountain, the RAW consists of a set of doubly-plunging anticlines referred to as the Rattles. The Olympic-Wallowa lineament has been controversial since it was first recognized by Raisz (1945) with two competing interpretations for the OWL: that of a major strike-slip fault and that of a series of thrusted anticlines. We will examine the RAW portion of the OWL focusing on geologic mapping from over the past 40 years and integrating that with published geophysical studies. We will show that the geologic structures of the RAW are north verging, thrusted anticlines that have had no strike-slip fault movement since at least the middle Miocene.