The name, Petaluma Gap, refers to the twenty-five kilometre opening in the coastal mountains that allows cold air from the Pacific Ocean to drift inland. This geographic feature influences the terroir of numerous wine growing regions across Northern [California](/region/california), none more so than the AVA that shares its name. Covering a geographic region of more than eighty-thousand hectares - around 2.5% of which is planted to vine, the Petaluma Gap appellation is uniquely defined by the wind; only plots within an area where recorded wind speeds average thirteen kilometres per hour are included in the AVA. The strength of the wind affects the vines by causing stomata on the leaves to close up, thus slowing the metabolic and transpiration processes and consequently, delaying the ripening of grapes. As well as the influence of wind, the climate here is characterised by warm afternoon sunshine with temperatures moderated by the marine air and fog that sweeps through the gap, and much cooler evenings. In some cases the diurnal temperature variation can be as much as fifty degrees Fahrenheit / ten degrees Celsius and this combination of factors results in fruit which is rich in flavour and naturally acidic. Grapes have been grown in this region for around one-hundred-and-fifty years and prior to its being established as an AVA in its own right, wines were produced under the vast [Sonoma Coast AVA](/ava/sonoma-coast-ava) label. [Pinot Noir](/pinot-noir) accounts for almost three-quarters of the appellation's vineyards with [Chardonnay](/chardonnay) and [Syrah](/syrah) the other varieties grown in quantity. The reputation of the area has led to an increasing number of prestigious [Sonoma](/county/sonoma-county) wineries looking to Petaluma Gap AVA as a source of exceptional fruit. Petaluma Gap [Pinots](/pinot-noir) are typically silky smooth with an understated richness and aromas of wild strawberry, cherry and rose petal.