The original Ridge wines from York Creek grapes were Petite Sirahs. Petite Sirah is frequently found in California planted in the same vineyards as Zinfandel (the same can be said of Carignane), and most California Zinfandels have at least some Petite Sirah included in the blend -- remember, a wine must only be 75% of a particular varietal to be labeled as that varietal in the United States, and most vintners like the tannic backbone and deep color that it gives to Zinfandel. It's probably called Petite Sirah because early grape growers thought that it had a genetic connection to Syrah, but in fact most Petite Sirah plantings have been identified as being Durif, a minor grape variety from the South of France. Several California wineries in addition to Ridge have bottled varietal Petite Sirah, but it usually does not make the most charming of wines. It certainly has not come into its own as a varietal like Zinfandel has.
In any event, the 2005 Ridge York Creek Zin has a healthy dollop of Petite Sirah -- 11%. I wish that I could tell you that I spotted the Petite Sirah character in this wine right off, but that would be a lie. About all I can claim is that I noticed that the wine was dark and that it fell far over on the Yum side of the Yum/Yuck scale.