DIFFERENCES IN TERROIRS OF WINE GRAPES IN OREGON, USA

In the United States, the state of Oregon ranks third number of wineries and fourth in production of wine. The different terroirs of the 18 AVA’s are based on differences in climate, geology, soils, elevations, and water holding capacity of the soils. The Willamette Valley AVA is mainly cool climate classification with three major geological units on the valley sides: volcanic soils (Columbia River Basalts; Jory Soil); marine sediments (shales and sandstones of the western foothills), and aged loess on basalt with pisolite concretions (Laurelwood Soils). The Columbia Gorge AVA has a cool climate to the west and warm climate at the east end. Geological diversity is found in volcanic soils of Underwood Mountain, Missoula Flood sediments close to the Columbia River, weathered volcanic debris flows of the upper Hood River Valley, sand dunes in Dallesport and loess at the east end. The Rocks of Milton Freewater in the northeast part of the state are mainly alluvium of gravels and cobbles in the valley bottom, but produce some of the finest wines in the United States.

In southern Oregon there are five regions: the Umpqua AVA with cool climate in the north and intermediate warm in the south and most of the vineyards being on fans and stream terraces; The Rogue Valley AVA has warm climate on the north side on mainly clay rich weathered volcanic soils and intermediate warm climate on the south side on mainly fans and stream terraces. The Applegate AVA is mainly intermediate warm climate on fans and stream terraces. The Illinois Valley is cool climate on mainly stream terraces and fans.