AT THE SOUTHERN END of the San Francisco peninsula, in the Santa Cruz mountains, a winery balances on the land formation from which it takes its name. Ridge produces excellent cabernet sauvignon and zinfandel from estate- grown grapes and grapes from most other California vineyard areas, because its own vineyard land is extremely limited. During harvest trucks laden with grapes from Napa, Sonoma, Amador and San Luis Obispo ascend one after the other through narrow hairpins leading from Cupertino to the winery, an ancient stone edifice, and surrounding redwood structures built a century ago for the purpose of wine-making.

A Monte Bello Ridge "claret" won a prize in the 1900 Paris Exhibition. Later the winery served as a source of sacramental wine during Prohibition, as many California wineries did,as well as a bootleg operation. In 1959 it and about

50 surrounding acres were bought

by a group of Stanford University

researchers and scientists with an

interest in wine, more as a scenic

weekend retreat. But the concentrated fruit grown in their Monte

Bello vineyard, at about 2,600 feet

elevation, proved unique, and wine

made from it was in great demand. In 1969 the owners hired winemaker Paul Draper, who had worked in Chile and had traveled and studied in France. Draper expanded the wine-making facilities and began to search the rest of the state for grapes of sufficient quality to emerge from Ridge's assiduous vinification as some of the best wines in California.

Ridge's star cabernet is the Monte Bello, a classic bordeaux-style, capable of considerable aging. The '81 Monte Bello has a big, earthy nose and a lush combination of cabernet sauvignon blended with 8 percent merlot. The wine reveals subtlety despite its youth. An older example, the '76 Monte Bello, had a more restrained nose, plus good acidity and fruit that overrode the tannins.

Ridge's less expensive cabernets include the Jimsonmare from nearby vineyards. The '82, recently released, is an elegant wine. It costs about $12. The '82 York Creek, made from Napa Valley grapes including 12 percent merlot and 2 percent cabernet franc, is deeper in color, with a lusher nose and cherryish fruit. The York Creek, sometimes described as peppery, sells for about $14.

Zinfandels reach their apotheosis at Ridge, one of the first California wineries to designate vineyards on the labels and the producer of as many as nine different zins. The least expensive is simply labeled Ridge and contains about 10 percent petite sirah. Others include San Luis Obispo, a big wine from the Paso Robles area; York Creek, Howell Mountain, and Geyserville, from grapes grown in the Alexander Valley.

Geyserville sells for about $10 and is worth it. A vertical tasting of some recent ones revealed common traits of elegance and balance rarely attained in zinfandel. The '83 is very fruity, with a lot of flavor and tannin. The '82 Geyserville reminded me of a spicy bordeaux. The '81 had a similarly restrained nose, but more body and fruit and a long finish. Like the '82, it needs time before drinking. The '80 Geyserville had the best nose of all, spicy and intense. It's a big, robust wine, not an "inky monster" out of California's recent past; it needs laying down and is a fine example of good zinfandel from a classic American winery.