How could Los Angeles have any influence on the wine industry? Well, it turns out that the start of California's commercial wine business was in LA.
The California missions run from San Diego's Mission, founded in 1769, to Sonoma's Mission in 1823. BTW, there were also missions throughout Baja California. The missions were known for planting wine grapes and making mission wine for church services and to serve at their own dinners.
You might consider the San Diego Mission as the oldest winery in the country. However, they haven't made wine there in a very long time, it was never really a commercial winery, and California wasn't part of the US at the time.