These rare red rocks were easily found, as he expected, on the surface of our Oakville vineyard by a visiting Boston geologist. Proof that one of the 5 soil types* present in our 25 acres washed down from Chiles Valley about 150 million years ago, as theorized.
Those really really interested in rocks and soils can access a study done several years ago for the Napa Valley Vintners, here. You'll be amazed at the geologic history of Napa Valley.
For the record, Mt. St. Helena is not an extinct volcano. It just looks like one.
* There are 34 soil series in Napa Valley. It's complicated.