Mendocino AVA was established on June 15, 1984 by the Bureau of Alcohol, Tobacco and Firearms (ATF), Treasury after reviewing a petition submitted by Mr. James A. Beckman, Vice-President of Guild Wineries and Distilleries, on behalf of 113 local viticulture industry members within the County, proposing a viticultural area named "Mendocino."
[8] Many wineries in the adjacent Sonoma, Napa and Lake counties source Mendocino grapes to blend into vintages labeled with their appellations.
At that time, there were 5,800 acres (9 sq mi) of grapes and nine wineries that produced 90,000 US gal (340,687 L) of wine in the Mendocino County.
At its widest point on the north end, the viticultural area is about 12 miles (19 km) wide, encompassing Redwood and Potter Valley with a hilly outcropping separating them.
The east fork is approximately 30 miles (48 km) inland from the Pacific Ocean and runs almost parallel to the coastline.
The west fork of the viticultural area, consisting of agricultural areas found in both the Navarro and Russian River watersheds, starts approximately one mile (2 km) south of a fork in the Navarro River and extends southeast approximately 34 miles (55 km).
The west fork also runs parallel to the Pacific coastline, approximately 15 miles (24 km) inland.
Also, it provides a grape growing season that has many warm, dry days, and generally cool nights.
The total average heat summation for Mendocino AVA for the period of April through October is 3,097 cumulative degree-days and is therefore classified as Region III.
[4] In comparison, Sonoma County, a major grape-growing region to the south of "Mendocino” displays a profound marine influence.
The total average heat summation for Sonoma County for the period of April through October is 3,046 cumulative degree-days, placing it just at the lower range of Region III for grape growing as defined by the University of California.
degree-days for Lake County for the months of April through October is 3,380 and is therefore classified at the higher range of Region II.