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 The geomorphology, soils, and climate of Columbia Basin vineyards are the result of a complex and dynamic geologic history that includes the Earth's youngest flood basalts, an active fold belt, and repeated cataclysmic flooding. Miocene basalt of the Columbia River Basalt Group forms the bedrock for most vineyards. The basalt has been folded by north-south compression, creating the Yakima fold belt, a series of relatively tight anticlines separated by broad synclines. Topography related to these structures has strongly influenced the boundaries of many of the Columbia Basin's American Viticultural Areas (AVAs). Water gaps in the anticlinal ridges of the Yakima fold belt restrict cold air drainage from the broad synclinal basins where many vineyards are located, enhancing the development of temperature inversions and locally increasing diurnal temperature variations. Vineyards planted on the southern limbs of Yakima fold belt anticlines benefit from enhanced solar radiation and cold air drainage. Most Columbia Basin vineyards are planted in soils formed in eolian sediment that is primarily derived from the deposits of Pleistocene glacial outburst floods. The mineralogy of the eolian sediment differs substantially from the underlying basalt. Vineyard soil chemistry is thus more complex in areas where eolian sediment is comparatively thin and basalt regolith lies within the rooting zone. The components of physical terroir that broadly characterize the Columbia Basin, such as those described above, vary substantially both between and within its AVAs. The vineyards visited on this field trip are representative of both their AVAs and the variability of terroir within the Columbia Basin.

Abstract This field trip guide covers a two-day trip to examine the characteristics of Columbia River Basalt Group flows and the Yakima fold belt. This field trip focuses on the main physical characteristics of the lavas, compositional variations, and evidence for their emplacement, and on the geometry of the anticlinal ridges and synclinal valleys of the fold belt and deformational features in the basalts.

Abstract The purpose of this field trip is to examine the sedimentology, sedimentary architecture, stacking patterns, and correlation of fluvial, coastal plain, deltaic, and shoreface to shelf deposits in the low accommodation Desert Member to Castlegate Sandstone stratigraphic interval (Campanian), Book Cliffs, eastern Utah. Traditional sequence stratigraphic models of falling stage deposits will be tested against an alternative sequence stratigraphic model that links the nonmarine to shallow-marine facies belts in both time and space. The trip will focus on the exceptional three-dimensional outcrop exposures in the Thompson Pass to Sagers Canyon region. At least eight sequence stratigraphic rock packages are identified and correlated, and these combine to form two progradational parasequence sets. The lower set comprises Desert Member rock packages 1-7, while the upper set comprises the SM/CC-2 rock package and overlying nonmarine strata of the Castlegate Sandstone. Rock package 7 is bounded above and below by coal-bearing, carbonaceous-rich zones. Correlation of the Upper and Lower Coal zones across the Crescent Canyon to Blaze Canyon region establishes a clear chronostratigraphic link between the nonmarine and shallow-marine strata of the Desert-Castlegate interval. The “fusing/welding” of rock packages 7 and SM/CC-2 with underlying cliff-forming sandstones in the South Face-Central to South Face-East region of Horse Heaven further demonstrates the chronostratigraphic link between the nonmarine and shallow marine. The alternative sequence stratigraphic interpretation of the Desert-Castlegate interval connects the nonmarine and shallow-marine facies belts in time and space, through correlation of coals, marine flooding surfaces, multi-storey channel complexes, and falling stage shallow-marine successions. “High-frequency” fluvial incision surfaces (sequence boundaries) merge to form a diachronous, lithostratigraphic contact between the nonmarine and shallow-marine facies belts. These contacts were previously defined as the “Desert SB” and “Castlegate SB” by J.C. Van Wagoner and were linked to longer term sea-level falls. Subsequent analysis of the “Desert SB” has revealed an amalgamation of “high-frequency” sequence boundaries that merge and split in a complex manner. Each “high-frequency” surface represents a shorter term portion of the longer term falling sea-level curve, which is equivalent to a parasequence-scale relative fall in sea level. “High-frequency” sequence boundary development, forced regression, and minor coastal plain aggradation occurs during the falling limb of the shorter term sea-level curve, followed by shallow-marine flooding, valley in-fill, coastal plain aggradation, and regional coal deposition during the rising limb of the shorter term sea-level curve. Individual nonmarine to shallow-marine chrono-slabs stack together. Inter-slab incision is rare in shallow-marine sections and where noted is relatively gentle (<3 m incision). In contrast, inter-slab incision is more significant in coastal plain settings due to reduced accommodation under falling stage conditions. The chrono-slab, parasequence-scale model for falling stage deposits in the Desert-Castlegate interval has four facies belts or zones. These record the transition from (i) nonmarine settings with single storey channels and scattered multistorey channel-fill complexes, to (ii) large-scale, multi-storey channel-fill successions (IVFs), to (iii) interbedded large-scale, multi-storey channel-fill successions (IVFs) and sandstone-rich proximal shallow-marine deposits, to (iv) proximal to distal, shoreface to shelf parasequences. This alternative chrono-slab model is likely applicable to falling stage deposits worldwide, especially those within a foreland basin setting. Ongoing research will extend the chrono-slab correlations outside of the study area and examine the relationship between relative sea-level history and chrono-slab thickness, facies belt length, and number of facies belts per chrono-slab.

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 In portions of Washington, Oregon, and Idaho, the Columbia River Basalt Group (CRBG) hosts a regional aquifer system that is the primary, and in many cases the only, water supply for numerous communities, small water systems, individual homes, industry, and agriculture. In much of the semiarid Columbia Plateau, portions of the CRBG aquifer system have seen significant water-level declines and do not appear to receive significant, if any, natural recharge. Aquifer horizons within the Columbia River basalt generally are associated with intraflow structures at the top (e.g., vesicular flow-top breccias) and bottom (e.g., flow-foot breccias, pillow lava and hyaloclastite complexes) of sheet flows. The interiors of thick sheet flows (in their undisturbed state) have extremely limited permeability and act as aquitards, typically creating a series of stacked, confined aquifers within the Columbia River basalt aquifer system. The dominant groundwater flow follows horizontal to subhorizontal pathways along individual, laterally extensive, interflow zones. Vertical groundwater movement through undisturbed basalt flow interiors is greatly restricted except where basalt flow interiors are disturbed (such as by folds or faults), truncated (such as by flow pinchouts and erosional windows), or where they are cross-connected by wells.