South Lake County boasts a landscape of contrast with its bucolic Callayomi Valley set like a Grandma Moses painting when seen from Middletown’s Rabbit Hill. Placed along the Mayacamas Mountain Range to the east of the valley is beautiful Cobb Mountain, almost 5,000 feet in elevation and encompassing about 74 square miles of mixed pine forests, chaparral, and oak woodlands.
While taking a geology hike (at Pepperwood Preserve) facilitated by Santa Rosa Junior College instructor and Department Chair of the Earth and Space Sciences Department, Rebecca Perlroth discussed Cobb Mountain. She stated, “The most concise information I can find is that the mountain is about 1.1 million years old, and is a rhyodacite dome made of similar composition to the solidifying magma (often called felsite) present below the Geysers geothermal field – the cooling magma that powers the geothermal engine there, heating the water to generate the steam, if that makes sense.
Rhyodacite is a composition rich in silica (SiO4) that typically produces explosive eruptions when gases are present. Basically, high silica magmas are really thick and viscous, trapping gases, which builds up pressure over time leading to violent explosion. The formation of a dome of this composition implies that perhaps all or much of the gas was released in an eruption prior to the magma oozing up to the surface, but that there was so much magma trying to get out that eventually, what remained just squeezed out. I’ve heard the comparison between viscous lavas and toothpaste: if you step on a tube of toothpaste, the toothpaste just sort of blobs out and doesn’t really have the ability to flow like one would think of lava flowing (like we see in Hawaii) so it just piles up around the “vent” or exit point.” So, although technically, Cobb is a volcano, its gasses were released in early eruption events and we can check that off of our list of things to worry about!
The Lake County Winegrowers website tells us that “Lake County’s past is very present” and has this to say about our volcanic wine-growing region, which includes Cobb Mountain and Mount Konocti, “Named for a volcanic caldera lake centered on the Clear Lake Volcanic Field, Lake County features some of the youngest volcanic soils in California. Two volcanoes dominate the landscape: Cobb Mountain (elevation: 4724 feet, 1440 meters) and Mt. Konocti (elevation: 4285 feet, 1306 meters). Both are home to vineyards.”
The Lake County Historical Society’s bulletin states that Cobb Mountain obtained its moniker from John Cobb. Cobb was born in Henry County, Kentucky on May 19, 1814, and was a farmer and river boater there. He suffered a tragedy when undisclosed circumstances occurred, and his first wife and two children died before 1848. After Cobb married his second wife, Esther E. Deming of Ohio, they started a family of six children. When he arrived in the Cobb region in October of 1853 with his wife and one of his children, the Cobb area was part of Napa County. Of all of the beautiful choices he was presented with when selecting a home, he chose Cobb. In 1854 John Cobb was voted Assessor of Napa County.
He lived in the area of Cobb Valley for nearly five years before moving down Middletown way to the Callayomi Valley where he farmed. After Lake County was divided from Napa County, Cobb worked the Callayomi and Guenoc Land Grants for Robert Waterman. Next, Cobb moved to the Stone House in what is now Hidden Valley, choosing this bucolic area in which to farm, and also leased some of the lands to settlers. Cobb moved locations during the ensuing years, but ended up living in Little High Valley at the Lea Neu Ranch. Cobb passed away on November 13, 1893, and rests at the Lower Lake Cemetery.
It appears that volcanoes like Cobb Mountain are multifaceted landforms: full of rich history, geologic wonders and beauty. Oh, and they make mighty fine wine, too!