The winery was built by Jack Riorda and a group of partners. Initially called Sunnyhill Winery, it was rechristened to Sunny St. Helena Winery a short time later.
Ceasare Mondavi father of Peter and Robert became a partner with Mr. Riorda. Peter and Robert Mondavi had their first winemaking experiences at Sunny St. Helena. In fact, it was here that they both experimented with cold fermentation for the first time. During this period, the winery produced one million gallons per year of bulk wine that was shipped east in rail cars for bottling by distributors.
The winery was sold to a small cooperative of Napa Valley growers and it functioned as a co-op for five years before being purchased by Charles Forni, a notable Napa Valley vintner of the time. The winery appears to have continued to operate as a cooperative at this time.