Sub-appellate wines are handled very much like appellate wines, with one more level of strictures. The 85% rule.
Where appellate wines need only be 75% of the stated varietal, 100% grown in the stated appellation, sub-appellate wines must be 85% of the stated varietal, 100% grown in the listed sub-appellation.
How does this look?
A 75% example reads: [PRODUCER], Cabernet Sauvignon, North Coast, California, 2015
An 85% example reads: [PRODUCER], Cabernet Sauvignon, Napa Valley, California, 2015
What is important to notice here is that Napa Valley is a recognized AVA that is sub-appellate to North Coast. So is Sonoma County AVA. So in these cases, the 85% rule applies to Napa Valley and Sonoma County labeled wines and all sub-appellations within (Knights Valley, Coombsville, Rutherford, etc…), where as a North Coast labeled wine is in the 75% rule and could potentially be mixing fruit from Napa and Sonoma allowing 25% to come from anywhere else in the state outside of the North Coast area.
The Central Coast wines fall under the 75% rule, but as soon as you state Santa Cruz Mountains, you are in the 85% territory. Same story goes for Sierra Foothills, Central Valley, and the South Coast.
To make things a bit more confusing, but also to assist in pedigree of what is in the bottle, if you label a wine in a sub-appellate like Rutherford, you need to list Napa Valley alongside Rutherford. This rule applies to wines from Napa Valley, Sonoma County, Paso Robles, and Lodi appellations.
An example would read: [PRODUCER], Cabernet Sauvignon, Oakville, Napa Valley, California, 2015
Once you have your head wrapped around the 75% rule, the 85% rule is actually quite easy to digest, almost as easy as the incredible wines that are made under these rules.