The Russian River Valley AVA does not strictly outline the path of the Russian River, which flows from Mendocino County south-by-southeast through Alexander Valley, makes an abrupt left at Healdsburg, and cuts west through rugged terrain to the Pacific Ocean. Rather like a heart in its shape, roughly 15 miles wide and tall, the AVA occupies a ‘sweet spot’ that’s cool, but not too cold. In the growing season, warm daytime temperatures plummet at night when fog regularly intrudes from the Petaluma Gap to the south, and the Pacific Ocean to the west. The northern border marks the point where the fog frequently sticks around a while longer in the morning, while Alexander Valley is already heating up.