Explain the American Viticultural Areas (AVA's)?

In 1978, the United States implemented the officially designated grape growing areasAmerican Viticultural Areas, or AVAs. These geographical designations are intended to be a means of showcasing a particular grape growing area's distinctions from one another. More specifically, in order for a potential AVA to be approved, the US government entails that evidence exists of its growing conditions such as climate, soil, elevation, and physical features are distinctive. American wine labels may identify a grape growing location or official AVA when a minimum of 85 of the grapes used for the wine come from the location identified on the bottle.

As of 2010, the TTB had recognized 198 AVAs throughout the United States. Lately, there have been an increasing number of sub-appellations designated to showcase even further distinction and specificity in a growing region.