stretches from Yorkville Highlands (located in a highland meadow straddling the upper Rancheria Creek and upper Dry Creek watersheds) through Boonville (located on Anderson Creek) and Philo (located on Indian Creek) to Navarro (located on Soda Creek). Rancheria, Anderson, Indian and Soda creeks are tributaries to the Navarro River, which flows north and west through the coastal range to the Pacific Ocean; Dry Creek flows south into the Russian River watershed in Sonoma County. The main stem of the Navarro River begins less than a mile south of Philo at the confluence of Anderson Creek and Rancheria Creek. The mouth of the Navarro is 10 miles (16 km) south of Mendocino, California. Encompassing 315 square miles (816 km²), the Navarro River watershed is the largest coastal basin in Mendocino County.
Such unique geography results in a wide diurnal range, with daily high and low temperatures occasionally diverging 40 or 50 degrees. This enables Pinot Noir growers to keep acid development in line with sugar and flavor formation through long, warm Indian summers. It also makes for superb Gewurztraminer and Riesling, giving rise to the valley’s annual Alsatian Varietals and Pinot Noir festivals
The area is not seismically active, though a minor fault runs along the Valley floor.