The Rocks District of Milton-Freewater or The Rocks of Milton-Freewater (known locally as "The Rocks District") is an American Viticultural Area (AVA) located in Umatilla County, Oregon and entirely within the Walla Walla Valley and the vast Columbia Valley AVAs. It was established as the nation's 228th, Oregon's eighteenth and Columbia Valley's eleventh appellation on February 9, 2015, by the Alcohol and Tobacco Tax and Trade Bureau (TTB), Treasury after reviewing the petition submitted by Dr. Kevin R. Pogue, a professor of geology at Whitman College in Walla Walla, Washington, proposing the viticultural area named "The Rocks District of Milton-Freewater."
The appellation lies entirely within the Oregon portion of the Walla Walla Valley AVA that partially expands across Walla Walla County. It is named for the city of Milton-Freewater, Oregon and a unique alluvial fan resulting in rocky soils with "baseball sized" basalt cobbles covering the earth, and is notable as being "the only AVA in the United States whose boundaries are defined by the soil type." Unique wine flavors are said to result from the mineral composition, hydrology, and temperatures of the volcanic rocks.
History The Rocks District of Milton–Freewater AVA is located on an alluvial fan of the Walla Walla River and derives its name from the cobblestone-rich soil near the town of Milton–Freewater, Oregon. The towns of Milton and Freewater were founded in the late 1800s and merged in 1951 to become Milton–Freewater. Washington State geologist and terroir consultant Kevin Pogue submitted the petition to TTB proposing an area named "The Rocks District of Milton-Freewater." The AVA petition was published for comment in the Federal Register in February 2014, and established in February 2015.
Labeling controversy The Rocks District lies only in the state of Oregon, unlike the Walla Walla Valley appellation. This has implications applying the appellation on wines produced in Oregon and Washington. Since Federal rules require wines to be fully finished in the state in which the AVA lies, only Oregon wineries, out of the more than 100 wineries in the Walla Walla Valley, would be permitted to use The Rocks District appellation on their labels. Also, all Oregon wineries processing 85% of the AVA's fruit in a vintage can display the appellation name on the labels. This caused some, labeled "prominent dissenters" by Wine Spectator'''s Harvey Steiman, to oppose the AVA. Other reactions were less pointed with some wine publishers using terms like "a bit of controversy" and "the location...creates some nuances". One of the same publishers said a "sub-appellation was ... inevitable given the uniqueness of the soils and resulting wines."
Terroir Climate The climate within The Rocks District has long been recognized as well suited to orchards and vineyards, which were first planted in the area in the late 1800s. Today, this area is the most productive orchard district in the Walla Walla Valley, as is apparent on the 1964 Milton-Freewater 7.5 minute topographic sheet, which shows most of the area of the AVA covered with the pattern of green dots used to designate orchards. Today, vineyards have replaced some of these orchards. The AVA lies primarily between elevations of , intermediate between the floor of the Walla Walla Valley and the Blue Mountain foothills. This range of elevations is ideal for maximizing daytime warmth while reducing frost and freeze risks related to the nocturnal temperature inversions that frequently affect the lower elevations of the Walla Walla Valley. This affect is apparent even within the boundaries of the AVA, as the higher, more southerly parts, closer to the town of Milton-Freewater, generally experience morning low temperatures that are a few degrees warmer than lower areas just a mile to the north. As this petition is being prepared, the Walla Walla Valley has just experienced five consecutive days with below average morning low temperatures (Oct. 4–8, 2012). Each morning, the freezing line fell somewhere between elevations of . Areas of the Walla Walla Valley below experienced temperatures as low as , while areas higher than generally remained above freezing. Temperatures within the AVA were near freezing each morning, but damage to crops was minimized by the use of wind machines. During this event, wind machines were largely ineffective at preventing damage due to sub-freezing temperatures at elevations below . The following climate data were obtained from the Western Regional Climate Center for weather station number 355593 (Milton). The current location of the station is 45°57' N, 118°25'W, which lies within the AVA. The average growing season (April–October) temperature computed for this station is for the period 1928-2005 and for the period 1981–2010. An average growing season temperature of lies within the preferred temperature range of a large number of wine grape cultivars. The average growing degree-days (50 °F, April–October) was 3053 for the period 1928–2005, which places the AVA within the cooler part of Winkler Region III. Average annual precipitation for the period 1928-2005 was . The average number of frost-free days is approximately 197. Average growing season temperatures and growing degree-days for the AVA are higher than in the more elevated Blue Mountain foothills to the east and lower than the Walla Walla Valley floor to the north and west. However, due to the affects of nocturnal temperature inversions, frost-free days are fewer to the west and north in valley floor locations and greater at higher elevations to the east. Eastward of the AVA, average annual precipitation increases dramatically due to affects of orographic lifting associated with the Blue Mountains. Westward of the AVA, precipitation gradually decreases toward the center of the Columbia Basin. The climatic features that are the most characteristic of the AVA are micro-climatic variations related to the area's cobbly soils. In vineyards where the surface of the ground is covered with basalt cobbles, extra heat is supplied to the vines via infrared radiation from the sun-warmed stones. This radiant heat raises the temperatures of grape clusters, particularly if they are hanging relatively low on the trellis. Studies conducted in this area have shown that mid-day temperatures of grape clusters suspended above basalt cobblestones can be warmer than those suspend at a similar height above grass-covered vineyards. Temperature has an important influence on grape composition and hence, on the flavors and aromas of wines The USDA plant hardiness zone is 7b.
Geology
The AVA lies within the Columbia Plateau geologic province, which is characterized by Columbia River Basalt bedrock formed from extremely thick accumulations of Miocene lava flows. In the area just east of the AVA, the Columbia River basalt has been folded into a broad anticline and uplifted to form the Blue Mountains. Erosion of the uplifted Blue Mountains supplied basalt-derived gravel, sand, and clay that were deposited in the synclinal basin to the west. These sediments now underlie much of the Walla Walla Valley, but they are now largely concealed by more recent deposits of fine sand and silt related to Pleistocene glacial outburst floods. All areas of the Walla Walla Valley below elevation, including the AVA, were repeatedly inundated by these floods, which deposited layers of sand and silt known as the Touchet beds, as well as large erratic rocks that had been encased in flood-borne icebergs. The granite-derived minerals in the flood sediments indicate that they were derived in part from outside of the Columbia Plateau, from rocks other than basalt.
In most parts of the Walla Walla Valley, the uppermost, soil-forming layer of sediment consists of wind-deposited silt, known as loess. The loess was sourced primarily from wind erosion of Pleistocene flood deposits in upwind areas such as the Umatilla Basin. Since the loess is derived from the flood deposits, it also contains minerals derived from non-basalt sources outside of the Columbia Plateau. In some parts of the Walla Walla Valley, modern streams have removed the loess and Pleistocene flood sediments, and deposited pebbles, cobbles, and boulders of basalt derived from bedrock exposures in the Blue Mountains. Deposits of these coarse-grained basaltic sediments are especially voluminous where Mill Creek and the Walla Walla River exit their Blue Mountain canyons and enter the broad floor of the Walla Walla Valley. In both of these areas, extensive alluvial fans have been constructed where the velocity and competency of the streams was reduced as a consequence of shallow stream gradients. Mill Creek's alluvial fan now hosts the city of Walla Walla, while the alluvial fan of the Walla Walla River is an agricultural district devoted to orchards and vineyards, and includes the site of the AVA. The geologic map shows that the AVA lies entirely within the Walla Walla River alluvial fan, within an area mostly mapped as "Quaternary younger alluvium." Records from water wells drilled within the Walla Walla River alluvial fan reveal a stratigraphy consisting of approximately of recent uncemented gravels overlying of mixed clay, sand, and cemented gravels, which in turn overlie basalt bedrock. Due to its small size and location within a single geologic landform, the stratigraphy of the AVA is remarkably consistent. Basaltic gravels are essentially the only substrate that would be encountered by even the most deeply rooted vines. This situation is quite different from vineyards of the Walla Walla Valley AVA that lie outside the AVA, where vines are growing in loess or fine-grained alluvium of varying thickness that overlies either basalt bedrock or Touchet beds.
Soils The most distinguishing feature of the AVA is the rockiness of its soils. Within the last ten years, the area within the boundary has come to be known as "the Rocks" region of the Walla Walla Valley AVA, but it has been famous for the fruitfulness of its stony soils for over 100 years. In an article entitled "Outsider's View of Freewater" in the December 1906 issue (p. 31) of Up-To-The-Times, a Walla Walla Valley magazine, George B. Sanderson wrote: "Rocks! Rocks!" I hear you say. Yes, but remember the best and largest strawberries grow in among these rocks, and such berries, too, as can't be raised in the East. The fruit trees are growing here in abundance. The luscious clusters of grapes are still on the vine, unhurt, as yet, by frost, and this is October." In the original Soil Survey of Umatilla County, Oregon, published in 1948, the soils of the AVA were mapped within the Yakima series as Yakima cobbly loam and Yakima gravelly loam. In 1985, these soils were re-classified within the new Freewater series as the Freewater very cobbly loam and Freewater gravelly silt loam. The urbanized cobble-rich soils of Milton-Freewater were classified as Freewater-Urban land complex. The most recent Umatilla County soil Survey, published in 1988, maps the distribution of the new Freewater series soils. The soils bordering the Freewater series that lie largely outside the boundary belong to the Walla Walla, Ellisforde, Yakima, Umapine, Hermiston, Onyx, and Oliphant series, which have been classified as silt loams in which cobbles are uncommon or absent.