Hi Petra. According to Geology Professor Terry Wright, "There was a volcanic episode (in Sonoma County) that lasted maybe between 8 million and 3 million years. These are called the Sonoma Volcanics, and Mount St. Helena was one of the last things that erupted. Sonoma Mountain and a lot of that territory and up through Mark West Canyon are all volcanic rock, which were formed during the time of the Sonoma Volcanics."

However, he says the chance of another volcanic period in Sonoma County is slim. "But Lake County has volcanic rocks as young as ten thousand years old. The USGS seems to think that that means it's an active volcanic field."

Cinnabar, the name given to mercury ore can only be found in areas of "recent" volcanic activity. Wright puts this in perspective: "The cinnabar deposits are basically associated with the Sonoma Volcanics, so they're part of the magma or the fluids that came up from deep within the earth. So by recent, that would mean a couple of million years, and that's pretty recent in terms of geologic time." The ore was found all along the Mayacama district, spanning Sonoma, Napa and Lake counties, especially along the ridge just south of the geysers. As you well know we have found this in your study area, which you now have in your garden.

The evidence for volcanic activity in your area is found all over the place so it’s not surprising there is a lot things left unexplained. We will have to take some pictures of the area near the dump and post them on our web site. Take Care…Don in creepy town