Napa Valley Vintners had the two "Welcome to this famous wine-growing region" signs built in 1949, when Napa Valley wasn't quite as famous as it is today. The Napa Sunday Journal ran a photograph of one of them - probably the Calistoga sign - in July 1950.

Roland Hauck designed the signs out of carved redwood, according to an article in the Jan. 5, 1967 Weekly Calistogan. Hauck had lived in Wooden Valley since 1935 on land settled by his wife's grandfather in 1863.

Source: Napa Valley Register, 29 October 2016

The phrase, "and the wine is bottled poetry," is from The Silverado Squatters by Robert Louis Stevenson, published in 1883. Here is the complete paragraph comparing California vintners to California prospectors.

"Wine in California is still in the experimental stage; and when you taste a vintage, grave economical questions are involved. The beginning of vine-planting is like the beginning of mining for the precious metals: the wine-grower also "Prospects." One corner of land after another is tried with one kind of grape after another. This is a failure; that is better; a third best. So, bit by bit, they grope about for their Clos Vougeot and Lafite. Those lodes and pockets of earth, more precious than the precious ores, that yield inimitable fragrance and soft fire; those virtuous Bonanzas, where the soil has sublimated under sun and stars to something finer, and the wine is bottled poetry: these still lie undiscovered; chaparral conceals, thicket embowers them; the miner chips the rock and wanders farther, and the grizzly muses undisturbed. But there they bide their hour, awaiting their Columbus; and nature nurses and prepares them. The smack of Californian earth shall linger on the palate of your grandson."