Geology Notes
Geology from Mars Estate on Howell Mountain
Rare rhyolite ground
Our vineyard sits on rhyolite, a hard, silica-rich volcanic flow within the Sonoma Volcanics. It's low in vigor and drains freely, so the vines struggle just enough to give small, concentrated berries rather than lush growth.
The green vein
About forty inches down, sandwiched between layers of volcanic ash, runs a seam of green alkaline clay, the fingerprint of an ancient hydrothermal lake that once sat beneath this ground. It's an unusual thing to find in Napa, and we think it's part of the mineral character tasters keep noticing in the glass.
Four vineyards in seven acres
When we dug soil pits across the property with geologist Brenna Quigley, we found not one terroir but four: clay-rich blocks that hold water without compacting, sandier ground Heidi points to for its balance, an iron-stained zone that runs technicolor red, and a pocket shaped by ancient andesite. The finished wine is the sum of those distinct voices.
A soil that's alive
In our soil pits, we found earthworms at every depth and vine roots threading straight through the holes in the volcanic bedrock. Rare rock matters, but rock with a deep, working soil alive on top of it matters more.