According to Wikipidia:
In California, 20% of the Zinfandel-growing counties hold 80% of the Zinfandel growing area; however, major producing areas such as San Joaquin County, Stanislaus County, and Madera County produce Zinfandel primarily for blends or jug wine.
Certain California regions are regarded as “exceptional” for Zinfandel, each with identifiable flavor characteristics.
- Amador has a reputation for big, full-bodied Zinfandel. These extra-ripe wines have been called jammy, briary, and brambly, having aromas of sweet berries.
- Although the Santa Cruz Mountains AVA in Santa Clara Valley produces Zinfandel from just 9 acres (3.64 hectares), the Zinfandel from that region is known for its complexity and depth.
- Sonoma county has a Zinfandel-producing land area second only to that of San Joaquin County. The county contains the warm Dry Creek Valley AVA, known for its juicy Zinfandel with bright fruit, balanced acidity and notes of blackberry, anise and pepper. Dry Creek Valley produces Zinfandel in a variety of styles ranging from the high-alcohol Amador style to balanced, spicy wines.
- San Luis Obispo, particularly the Paso Robles AVA with its hot days and cool maritime evenings, produces Zinfandel known for being soft and round.
- While the Napa Valley AVA is known primarily for its Cabernet Sauvignon, Merlot, and Syrah, Napa also produces Zinfandel wines described as plummy and intense, tasting of red berry fruits with cedar and vanilla. Zinfandel in Napa tends to be made in a claret style like red Bordeaux.
- The Russian River Valley generally produces well during warm vintages. Otherwise, the grapes do not fully ripen, leaving the wines with excessive acidity. The area has mostly “old vine” Zinfandel, characterized as spicy and somewhat lower in alcohol than Zinfandel from other regions.
- Mendocino County Zinfandel wines have been considered high quality, but they are less known because they are not heavily marketed.
- Lodi has some of the oldest Zinfandel vines in California. While often used for White Zinfandel production, in the red style, Lodi Zinfandels have a reputation for being juicy and approachable.