The Geological Society of America Field Guide 15 2009 Folds, fl oods, and fi ne wine: Geologic infl uences on the terroir of the Columbia Basin Kevin R. Pogue Department of Geology, Whitman College, Walla Walla, Washington 99362, USA 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 fl ood basalts, an active fold belt, and repeated cataclysmic fl ooding. 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 infl uenced the boundaries of many of the Colum- bia 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 inver- sions and locally increasing diurnal temperature variations. Vineyards planted on the southern limbs of Yakima fold belt anticlines benefi t 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 fl oods. 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 fi eld trip are representative of both their AVAs and the variability of terroir within the Columbia Basin. INTRODUCTION duction of a wine and account for its distinctive characteristics. The term is also invoked to describe the sensory qualities of a This fi eld trip focuses on the variations in vineyard geology wine that relate it to specifi c place, an attribute wine writer Matt and climate that have produced a broad range of physical terroirs Kramer has described as a wine’s “somewhere-ness.” within the Columbia Basin, the region of eastern Washington and It is tempting, especially for earth scientists, to overempha- northeastern Oregon that lies east of the Cascade Range and north size the physical components of terroir such as geomorphology, and west of the Blue Mountains and is generally below 600 m bedrock, soils, and climate (e.g., Wilson, 1998; Fanet, 2004). in elevation (Fig. 1). The French word terroir is commonly used However, the cultural environment of a vineyard and winery also to refer to the sum of all environmental factors that affect the pro- heavily infl uences the unique combinations of fl avors, aromas, Pogue, K.R., 2009, Folds, fl oods, and fi ne wine: Geologic infl uences on the terroir of the Columbia Basin, in O’Connor, J.E., Dorsey, R.J., and Madin, I.P., eds., Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacifi c Northwest: Geological Society of America Field Guide 15, p. 1–17, doi: 10.1130/2009.fl d015(01). For permission to copy, contact [email protected]. ©2009 The Geological Society of America. All rights reserved. 1 2 Pogue colors, and textures that defi ne a wine’s somewhere-ness. In U.S. grape and wine producers could petition to have their region Europe, both viticulture and winemaking have evolved over hun- formally recognized as an American Viticultural Area (AVA). dreds of years in response to the unique physical terroir of each The TTB regulations legally defi ne the geographic boundaries region. Viticulturalists have determined the varieties, known as of AVAs, but no restrictions are placed on the variety of grape cultivars, which are best suited to their region (e.g., Pinot Noir or how it is grown. To be approved, a petition for a new AVA in Burgundy) and how best to farm them. Winemakers have must contain “evidence that the geographical features of the area developed techniques designed to highlight the qualities of their produce growing conditions which distinguish the proposed area region’s cultivars. Thus, the physical terroir and the cultural ter- from surrounding areas” (Section 4.25a(e)(2), Title 27, Code of roir work in harmony to produce wines of a unique character. Federal Regulations). If the name of an AVA appears on a wine Over time, various regions have become associated with distinc- bottle, TTB regulations require that eighty-fi ve percent of the tive styles of wine. grapes used to make the wine must come from within the bound- Recognizing that wines derive much of their value from their aries of the AVA, but place no other restrictions on winemaking unique terroirs, the French government in 1935 created a system techniques. that legally defi ned viticultural regions. Each wine-producing Due to the substantial variations in climate and soils, it is region, known as an appellation, has rigid guidelines that legally unreasonable to expect that all wines produced from grapes defi ne or restrict the cultivars and the viticultural and winemak- grown within the boundaries of a particular AVA will possess ing techniques that may be utilized. Other European countries a shared set of sensory characteristics that defi ne a somewhere- have followed suit, establishing their own guidelines for legally ness or “taste of place.” The defi ning physical characteristics of recognized wine producing areas. In 1978, the U.S. Bureau of an AVA are therefore best viewed as a broad theme that unites a Alcohol, Tobacco, and Firearms (now the Alcohol and Tobacco unique collection of terroirs. True terroir can only be expressed at Tax and Trade Bureau, or TTB) established a system whereby the scale of individual vineyards. 100 km N 100 miles CAN US R A N G E Seattle WA ID Columbia Valley AVA Area of boundary figure 2 C O L U M B I A C A S C A D E WA B A S I N OR M O U N T A I N S Portland Columbia Gorge AVA boundary B L U E Figure 1. Shaded relief map showing locations of the Columbia Basin and Columbia Valley American Viticultural Area (AVA). ID— Idaho; OR—Oregon; WA—Washington. Geologic infl uences on the terroir of the Columbia Basin 3 Although wine grapes have been cultivated in the Colum- the western boundary of the Columbia Valley AVA along the bia Basin since the 1800s, there were still fewer than 10 com- Columbia River (Figs. 1 and 2). mercial wineries in the northwestern United States in 1970 (Gregutt, 2007). In the 1980s, the number of wineries increased Geologic Setting dramatically, and many new vineyards were planted, primar- ily in the Yakima Valley, an established agricultural area with During the Miocene, between 17 and 6 Ma, ~174,000 km3 of a relatively plentiful supply of irrigation water. In 1983, a peti- continental tholeiitic basalt erupted from fi ssures in southeastern tion by Yakima Valley vineyard owners and winemakers was Washington, northeastern Washington and western Idaho (Tolan approved, and the Yakima Valley became the fi rst AVA in the et al., 1989). At least 300 individual fl ows eventually covered Columbia Basin (Fig. 2). The next year, the petition for the more than 164,000 km3 of Washington, Oregon, and Idaho, a Columbia Valley AVA, was approved. Its authors designated the region known as the Columbia plateau (Fig. 3). The thickness boundaries to encompass most of the region within the Colum- of the basalt exceeds 4 km in the central part of the plateau bia Basin with viticultural potential, principally low elevation (Reidel et al., 1989). The course of the ancestral Columbia River regions with an arid to semi-arid climate (Fig. 1). Since 1984, followed the northern and western margin of the basalt, which seven more AVAs have been designated in the Columbia Basin. rerouted rivers draining eastward from the crest of the Cascade Six of these—the Walla Walla Valley, Red Mountain, Horse Range. Fluvial and lacustrine sediments overlying and interbed- Heaven Hills, Rattlesnake Hills, Wahluke Slope, and Snipes ded with the Columbia River Basalt of the western Columbia Mountain—lie within the confi nes of the Columbia Valley AVA plateau are known as the Ellensburg Formation. The Ellensburg (Fig. 2). The Columbia Gorge AVA, approved in 2004, abuts Formation consists of both laterally extensive Cascade-derived Columbia Mt. Ranier River Wahluke Slope AVA Rattlesnake Hills AVA River R A N G E area of Figure 10 Yakima Valley AVA Red Mtn. AVA Snake area of Figure 11 Mt. Adams Snipes Mtn. AVA Walla Walla Horse Heaven Hills AVA Valley AVA area of Figure 9 River C A S C A D E area of Figure 12 Columbia Columbia Gorge AVA Mountains Mt. Hood Blue field trip stop N 75 km field trip route 50 miles Figure 2. Shaded relief map of the Columbia Basin showing the fi eld trip route, locations of the Columbia Gorge American Viticultural Area (AVA), and locations of the seven sub-AVAs of the Columbia Valley AVA. 4 Pogue volcaniclastic debris-fl ow deposits and polymict conglomerate initially able to keep pace, creating the water gaps still utilized deposited within the channels of the ancestral Columbia River by these rivers (Fig. 5A). However, the combination of the rising (Smith, 1988). The Columbia River Basalt Group and Ellensburg anticlinal ridges, volcanism, and isostatic subsidence of the thick Formation form the bedrock in all of the vineyards visited on this pile of basalt centered in the Pasco Basin eventually steered the fi eld trip as well as in the vast majority of the Columbia Valley rivers to the east along synclinal axes (Fecht et al., 1987) (Fig.