Trellis Talks: From Caldera to Cabernet: The Ancient Lake Beneath Coombsville

In this episode of Trellis Talks, Caleb Mosley sits down with soil scientists Dr. Paul Anamosa and Dr. Nick Madden to explore their 2023 paper, “The Other White Rock in Coombsville Vineyards.” The conversation unpacks the geological mystery and viticultural significance of diatomaceous earth found in the Coombsville AVA—a lightweight, silica-rich sediment formed from freshwater algae in an ancient caldera lake. Anamosa and Madden discuss how these unique soils, often mistaken for volcanic ash or bentonite, impact vine growth, emphasizing their low pH, high aluminum toxicity, and unusual water retention characteristics. They explain how proper soil analysis and management—particularly the use of gypsum and lime—are crucial for successful vine development in these challenging conditions.
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The episode also delves into the broader story behind their collaboration, from international development work to building one of Napa’s most extensive soil pit databases. As Paul transitions into retirement, he reflects on the importance of mentorship and passing on deep technical knowledge to the next generation of consultants like Nick and their colleague Scott Nippelmeyer. Their combined efforts promise a new era of viticulture grounded in science, innovation, and deep respect for Napa Valley’s complex terroir.