The U.S. Appellation System

The first time I learned about the U.S. Appellation System was when I took the Introduction to Winemaking, the online UC Davis Course that is open to anyone desiring to learn more about winemaking. It is also the prerequisite for the online Certification program.
In the United States, grape growing regions can be designated as an American Viticultural Area or AVA. The Wine Institute is host to the AVA database where all of the recognized American grape growing regions can be found. It is a handy database that lists the AVA by name, size, state, and effective date.This designation is modeled after the European regional system, however, unlike France, the AVA is only indicative of the geographic origin of the fruit and is not necessarily viticulturally or enologically distinct. The name proposed for the formation of a new AVA is one that is (or was at one time) known for the area locally or nationally and has recognized boundaries.¹
Here is a link to a really good introduction to the BATF regulations written so that anyone can understand it: The BATF, Wine Labels, Vintages and Wine Regions
U.S. Appellation Rules for Wine Labels:

• Political area                          --->75%
• AVA                                        --->85%
• Vineyard designation             --->95% from named vineyard                                                      requires AVA
• Estate bottled                         --->100% from vineyards owned or                                                       controlled by the winery                                                      (both must be in an AVA also named)
• Grape Variety                          --->75%
• Vintage                                    --->95% if year stated                                                      (since June 2006, 85% if county or                                                      multi-county AVA or state)
• Produced/Made and bottled by--->75% must be fermented, aged and                                                      bottled at indicated location)
• Cellared/Vinted and bottled by--->Not necessarily fermented at                                                      indicated location
• Reserve                                  --->no legal meaning in the U.S.
• California and Oregon have more stringent rules

The appellation that can be used on the wine is governed by the source of the fruit, not the location of the winery. But the winery location will also be shown, usually at the bottom of the label (“Produced and bottled by…”). For example in California, wines that are made from fruit from several different places are often given a “California” geographic indication (which by law would require only 75% California fruit, but by the stricter California law must contain 100% California fruit).
1. From Introduction to Winemaking (092VID251), U.C. Davis Online Course, 2009.