Deformation of the continental flood-basalt in the westernmost portion of the Columbia Plateau has resulted in regularly spaced anticlinal ridges. The periodic nature of the anticlines is characterized by dividing the Yakima fold belt into three domains on the basis of spacings and orientations: (1) the northern domain, made up of the eastern segments of Umtanum Ridge, the Saddle Mountains, and the Frenchman Hills; (2) the central domain, made up of segments of Rattlesnake Ridge, the eastern segments of Horse Heaven Hills, Yakima Ridge, the western segments of Umtanum Ridge, Cleman Mountain, Bethel Ridge, and Manastash Ridge; and (3) the southern domain, made up of Gordon Ridge, the Columbia Hills, the western segment of Horse Heaven Hills, Toppenish Ridge, and Ahtanum Ridge. The northern, central, and southern domains have mean spacings of 19.6, 11.6, and 27.6 km, respectively, with a total range of 4 to 36 km and a mean of 20.4 km ( n = 203). The basalts are modeled as a multilayer of thin linear elastic plates with frictionless contacts, resting on a mechanically weak elastic substrate of finite thickness, that has buckled at a critical wavelength of folding. Free slip between layers is assumed, based on the presence of thin sedimentary interbeds in the Grande Ronde Basalt separating groups of flows with an average thickness of roughly 280 m. Many of the observed spacings can be explained by this model, given that: (1) the ratio in Young’s modulus between the basalt and underlying sediments E/E o ⩾ 1,000, (2) the thickness of the Grande Ronde Basalt was between 1,200 and 2,300 m when the present wavelengths were established, and (3) the average thickness of a layer in the multilayer is between 200 and 400 m. The lack of well-developed anticline-syncline pairs in the shape of a sinusoid may be the result of plastic yielding in the cores of the anticlines after initial deformation of the basalts into low amplitude folds. Elastic buckling coupled with plastic yielding confined to the hinge area could account for the asymmetric fold geometry of many of the anticlines.

Abstract Washington State is second only to California in terms of wine produced in the United States, and some of its vineyards and wines are among the world’s best. Most Washington vineyards are situated east of the Cascades on soils formed from Quaternary sediments that overlie Miocene basaltic rocks of the Columbia River Flood Basalt Province. Pleistocene fluvial sediments were deposited during cataclysmic glacial outburst floods that formed the spectacular Channeled Scabland. Late Pleistocene and Holocene sand sheets and loess form a variable mantle over outburst sediments. Rainfall for wine grape production ranges from ~6-18 in (150-450 mm) annually with a pronounced winter maximum and warm, dry summers. This field trip will examine the terroir of some of Washington’s best vineyards. Terroir involves the complex interplay of climate, soil, geology, and other physical factors that influence the character and quality of wine. These factors underpin the substantial contribution of good viticultural practice and expert winemaking. We will travel by bus over the Cascade Mountains to the Yakima Valley appellation to see the effects of rain shadow, bedrock variation, sediment and soil characteristics, and air drainage on vineyard siting; we will visit the Red Mountain appellation to examine sites with warm mesoclimate and soils from back-eddy glacial flood and eolian sediments; the next stop will be the Walla Walla Valley appellation with excellent exposures of glacial slackwater sediments (which underlie the best vineyards) as well as the United States’ largest wind energy facility. Finally, we will visit the very creatively sited Wallula Vineyard in the Columbia Valley appellation overlooking the Columbia River before returning to Seattle.

ABSTRACT The Miocene Columbia River Basalt Group (CRBG) covers a large part of Oregon, Washington, and Idaho and is one of the youngest and perhaps the best studied flood-basalt province on Earth. Decades of study have established a regional strati-graphic framework for the CRBG, have demonstrated the CBRG flows can be correlated with dikes and vents, have documented a wide variety of physical features within the CRBG flows, and have demonstrated that many characteristics of the CRBG are recognizable throughout its extent. Detailed studies of individual flows and their feeder dikes have allowed the development of models for the emplacement of voluminous basaltic lava flows. The interplay between the regional structure, contemporaneous deformation, preexisting topography, and paleodrainage systems helped to control the emplacement of individual CRBG flows. These features have also affected the nature of late Neogene sedimentation in the region covered by basalt flows. Finally, the distribution of sediments within the CRBG and the character of the intraflow and interflow structures have played a significant role in the development of aquifers within the CRBG. In this paper we present an overview of the regional aspects of the stratigraphy, structural geology, tectonics, and hydrogeology of the CRBG.