Willamette Valley Geology 101 | Youngberg Hill
As farmers, we wine grape growers have a strong interest in the soils our vines are planted in. When we explain to guests the different characteristics of our soils, we are often asked how the soils got there and why they are so different from one another. During such a discussion with some recent guests, we were fortunate to have among them a geologist who was visiting. He not only took a strong interest in our explanation, but had additional information to share as well. For all of our “dirt-geek” readers, and for those who just want to learn more, his research points can be read in the following pdf . We are thankful to have such interested and passionate guests who want to join the discussion about wine farming, and welcome your comments on the topic of soil in the Willamette Valley!
The age, geologic events and resulting deposits from the three geologic episodes, Early Volcanic Arc, Coastal Range Sediments, and Coastal Range Volcanoes are discussed in detail. I included the discussion of the Early Island Arc episode because volcanic rocks from that episode were likely the source of the Coastal Range episode marine sediments that the Natasha vineyard grapes grow on. Assuming that is the case, I would speculate that because the volcanic rocks deposited during the Early Island Arc episode were more compositionally diverse (see explanation in the PDF Figure 4) one would expect that the Coastal Range marine sediments and soils derived from them would contain a greater, possibly richer suite of minerals which would be available to the Natasha grapes.
The material issuing for the Coast Range Volcanoes on the other hand is described as basalt and diabase (a coarse-grained version of basalt). In addition to the fact that these basalts form a rocky soil under the Jordan vineyard at Youngberg Hill, basalt may yield a more limited suite of minerals to support the Jordan grapes. I would be curious this sort of nutrient difference between the two vineyards is observed.
In summary, the Early Volcanic Arc episode began about 52 million years ago (mya) and resulted in volcanic rocks that were the likely source of Coastal Range marine sediments (sandstones, siltstones, etc.) that began to be deposited about 50 mya and form the soils for the Natasha vines. Coastal Range Volcanoes began extruding and intruding basalts about 45 mya and these basalts form the soils for the Jordan vines.