A comment from the venerable Mr Ian Brand reinforced my suspicions that some small parcel of ancient Mourvèdre from the Valley of Heart’s Delight must still exist.
On Cellartracker, there is an old-vine Santa Clara Valley Mourvèdre/Zinfandel from Cronin Wines. The Cronin “Wolfinbarger Vineyard” single-vineyard red wine included the 1997 and 1998 vintages.
Santa Cruz Mountains-based winemaker Duane Cronin primarily focused on Burgundian varieties, but a few oddities were bottled as well. Production of Cronin wines ended with the 2000 vintage, and Duane Cronin passed away in 2007.
Mr Dave Tong’s old blogspot site includes a map of several Santa Clara vineyards, including the “Wolfinbarger Vineyard” in San Martin, CA.