Following up on my recent visit to a geological society meeting, I paid a visit to Portland State University geologist Scott Burns for more information on the soils and rocks of the northern Willamette Valley.
First, Burns' office is filled with rocks of all kinds. I think if you look up the word rockhound, you'll see his picture.
Second, Burns clearly loves wine and loves talking about wine and geology. So I asked him a few questions to get a little more insight on the local territory.
I knew our geology here is either volcanic basalt or ocean sediments. But where did the soils on the basalt come from? I wasn't sure if they were wind-blown deposits, but in fact our volcanic soils are mostly eroded basalt. Hence their red color and, given their age of 14 million years, low fertility.
And what about the "bathtub ring" left over from the Missolua floods 10,000-15,000 years ago? These floods covered the Willamette Valley floor with rich "Woodburn" deposits up to a height of 400 feet. However, most of these deposits settled below 200 feet or so, with rapidly thinning deposits the higher you go up to the bathtub ring.
So the best vineyard land in this part of Oregon is above the flood deposits, at least 200-250 feet and ideally higher still. However, there are places below 400 feet particularly in the Eola Hills with shallow and infertile soils that suggest the bathtub ring (or maximum height of the Missolua floods) might vary depending on location.
I'll investigate that further as I delve into the further refinement and reclassification of many soils in this area. Stay tuned.