Mendocino County has a wide range of viticultural mesoclimates that are influenced by the county's diversity in climatic and geography. On the eastern borders of the county is the Mayacamas Mountains separating it from nearby Lake County and the influences of the large Clear Lake. Within the county, the Mendocino Range segment of the larger California Coast Ranges essentially divides the region into two climatic spheres. The land to the west of the ranges, closest to the coast tend to have more maritime climate that includes more cooling and rain influences from the Pacific ocean. Among the wine regions in this cooler area are the Mendocino Ridge, the Anderson Valley and the Yorkville Highlands AVAs. East of the ranges, the climate turns warmer and more Mediterranean around Ukiah and along the path of the Russian River as it makes its way southward to Sonoma County. Among the Mendocino wine regions in this warmer area are the Redwood Valley, Potter Valley, Cole Ranch, McDowell Valley, Covelo, Dos Rios AVAs as well as most of the large general area Mendocino AVA. In this eastern region, the ranges serve as a type of rain shadow and barrier to the cool Pacific fog which leaves the climate during the growing season much drier and warmer with ratings of Region III and IV on the Winkler scale.