Another virtue of the markets is having the chance to taste before you buy. A few tables down from the Portellos' almonds, Peggy and Michael Henwood of Henwood Estates encourage sampling of their artisan olive oils, made on their ranch near Marysville. Tidbits of bread saturated with green-golden oil, pressed days before, inspire wine-like descriptors: herbaceous and creamy, with slight tannin on the finish.

Farmers' markets serve as inspiration for home chefs and prominent chefs alike. Thursdays are market day for Bradley Ogden, chef/owner of Larkspur's Lark Creek Inn, who, in summer, spends $4,000 a week at market. Ogden has been frequenting the Marin market, located beside the Frank Lloyd Wright-designed Civic Center, since its founding in 1983. Surveying the market's cornucopia, he beholds a 1000-karat Hachiya persimmon and proclaims triumphantly, "A steamed pudding . . . with a blood orange curd!" Many markets combine old-world influences, like the one in Old Town Oakland. There you'll find everything from Russian pierogi to exotic Asian greens. The market's nestled between rows of Victorians and the revitalized Swan's, an old-style open market. A half-dozen languages meld with the calming notes of "Destiny the Harpist," who plucks her harp at many Bay Area markets. When Old Oakland comes alive at 8 a.m., so do the products. Indignant chickens and chukars (partridges) are extricated from cages while catfish are scooped from a tank on the back of a pickup. While fins and feathers fly, farmers stack salted duck eggs stained iridescent magenta, lest you confuse them with baluts (white fertile duck eggs).

Old Oak is "the proletarian market," says Sandro Rossi, who owns Caffé 817 around the corner, a popular retreat for farmers and shoppers. Rossi searches the stalls for a savoy cabbage for his Tuscan bean soup and dates to stuff with walnut meats for dessert. For the Florence native, markets are a way of life. Saturdays find Rossi at what he calls "the market of nobility—the social event of the week," the San Francisco Ferry Plaza market, on the Embarcadero.

On a typical Saturday at the Ferry Plaza gathering you might see the city's poet laureate Lawrence Ferlinghetti or symphony conductor Michael Tilson Thomas wandering among the fashionable throngs lined up for a bite at the Hayes Street Grill or Rose Pistola booths. From May through November, Ferry Plaza hosts free programs introducing consumers to farmers and chefs. One of those farmers is Art Lange of Honey Crisp Farm in Reedley, where he cultivates dwarf peaches, plums, and nectarines.

As the fresh stone-fruit season is so fleeting, Lange has devised a sulfur-free method of preserving the summer sweetness in micro-thin slices, using honey and apple juice. His dried Snow Queen nectarines are so addictive that one customer thinks nothing of buying $150 worth at a pop.

Farmers' markets can sustain the vitality of city centers. Such is the case with San Luis Obispo's market, half a block from the mission founded by Father Junipero Serra. The evening market on Higuera Street is the centerpiece of an urban success story. During the 1970s, downtown business took flight to suburban malls; the only action left on Thursday nights was cruising. The city tried holding volleyball tournaments, but it took someone setting up a barbecue in the street to get things cooking. Others followed suit, the downtown association invited the farmers, and the market was born in 1983.

Today on Thursday nights, the aroma of smoked meat and calzone wafts down five blocks of farmers and sundry merchants. The market transforms into one big street party, with bands battling for shoppers' attention. Under the lights, you can find sweet Chantenay carrots from Domingo Farm in Arroyo Grande and burdock root, which is good for ridding the body of excess fluid. To rehydrate yourself, there's apple zinfandel juice from Chadmark Farms. Mike Cirone trucks in Blenheim apricots and tiny lots of 50 heirloom apple varieties and tropical fruits adapted to the local clime, including the white sapote and cherimoya, from nearby See Canyon. No surprise, San Luis Obispo was honored by the National Trust for Historic Preservation for having one of the five best Main Streets in the nation.

The boast for the state's largest farmers' market goes to sunny downtown Santa Monica. Some 90 farmers gather there on Wednesday mornings. Professional chefs and their domestic counterparts wend their way along Arizona Street near the Third Street Promenade, pushing carts of ingredients for the evening meal. Chef Mark Peel of Campanile tracks down lamb's- quarters. Once a pesky weed, it now holds uncommon appeal. "We call it wild spinach; otherwise people expect a meat dish," says Peel. Bunches of arrow-headed leaves join lipstick peppers, squash blossoms, and sweet broccoli sprouts in Peel's cart.

At market, culinary trends evolve over casual conversation. Chefs track down heirloom seeds, farmers place them in the ground and bring the results to market, and consumers end up with a direct connection to the freshest produce and stories to be had. Jefferson would approve.