What mountain range is located between Sonoma and Napa?

The Mayacamas Mountains serve as a natural boundary between Sonoma and Napa Valley, playing a significant role in the geographical and climatic delineation of these two renowned wine regions in California. This mountain range influences the microclimates within both valleys, contributing to the diverse terroirs that affect vine growth and grape quality.

The range not only provides elevation but also impacts weather patterns, shielding Napa Valley from some coastal influences while allowing for warm afternoons, which are ideal for ripening grapes. This is particularly important for the red varietals that thrive in Napa, like Cabernet Sauvignon.

In contrast, the Vaca Mountains, located on the eastern side of Napa Valley, and the Santa Cruz Mountains, further south, do not directly separate Sonoma from Napa. The Coast Range, which runs along the California coastline, is also farther away and does not specifically serve as a divider between these two valleys. Thus, the Mayacamas Mountains are the correct answer as they directly define the boundary and have a considerable influence on the viticulture of both regions.