This year, four Northern California wineries are celebrating their 40th anniversaries—a notable achievement in a competitive Napa-Sonoma world constantly buffeted by the vagaries of nature and consumer’s desires. Davis Bynum Winery,the first to produce single-vineyard Pinot Noir from the Russian River Valley; Chateau St. Jean, which established European-style vineyard-designated wines in California; Domaine Chandon, the first French-owned producer of sparkling wine in Napa Valley; and the family-owned Cakebrea…