The Petaluma Gap is a geographical region in Sonoma County, California

Sonoma County, California

Sonoma County, located on the northern coast of the U.S. state of California, is the largest and northernmost of the nine San Francisco Bay Area counties. Its population at the 2010 census was 483,878. Its largest city and county seat is Santa Rosa....

 which extends in a band from the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 to San Pablo Bay

San Pablo Bay

San Pablo Bay is a tidal estuary that forms the northern extension of San Francisco Bay in northern California in the United States. Most of the Bay is shallow; however, there is a deep water channel approximately in mid bay, which allows access to Sacramento, Stockton, Benicia, Martinez, and...

. It is an area of low land 22 to 31 miles (35 to 50 kilometers) wide in the coast ranges of the northern San Francisco Bay Area

North Bay (San Francisco Bay Area)

The North Bay is a subregion of the San Francisco Bay Area, in California, United States. The largest city is Santa Rosa. It is by far the least populous and least urbanized part of the Bay Area...

. The western edge of the gap is located in the coastal lowlands between Bodega Bay

Bodega Bay

Bodega Bay is a shallow, rocky inlet of the Pacific Ocean on the coast of northern California in the United States. It is approximately across and is located approximately northwest of San Francisco and west of Santa Rosa...

 and Tomales Bay

Tomales Bay

Tomales Bay is a long narrow inlet of the Pacific Ocean in Marin County in northern California in the United States. It is approximately 15 miles long and averages nearly 1.0 miles wide, effectively separating the Point Reyes Peninsula from the mainland of Marin County. It is located...

. The eastern edge of the gap is located at San Pablo Bay around the mouth of the Petaluma River

Petaluma River

The Petaluma River is a river in the California counties of Sonoma and Marin that becomes a tidal slough near its mouth. It springs from farmlands southwest of Cotati and flows generally southward through Petaluma's old town and of tidal marshes to end in northwest San Pablo Bay.-History:The word...

. The city of Petaluma

Petaluma, California

Petaluma is a city in Sonoma County, California, in the United States. In the 2010 Census the population was 57,941.Located in Petaluma is the Rancho Petaluma Adobe, a National Historic Landmark. It was built beginning in 1836 by General Mariano Guadalupe Vallejo, then Commandant of the San...

 is near the center of the gap.

The Petaluma Gap affects wind patterns (and thus microclimate

Microclimate

A microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet or as large as many square miles...

s and air quality) in the San Francisco Bay Area

San Francisco Bay Area

The San Francisco Bay Area, commonly known as the Bay Area, is a populated region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses metropolitan areas of San Francisco, Oakland, and San Jose, along with smaller urban and rural areas...

. Fresh marine air generally blows eastward through the gap, branching into southward and northward streams which blow toward the Carquinez Strait

Carquinez Strait

The Carquinez Strait is a narrow tidal strait in northern California. It is part of the tidal estuary of the Sacramento and the San Joaquin rivers as they drain into the San Francisco Bay...

 and Santa Rosa

Santa Rosa, California

Santa Rosa is the county seat of Sonoma County, California, United States. The 2010 census reported a population of 167,815. Santa Rosa is the largest city in California's Wine Country and fifth largest city in the San Francisco Bay Area, after San Jose, San Francisco, Oakland, and Fremont and 26th...

 respectively. The southward stream brings marine air overland into the central Bay Area from the northwest. Warm air rises from the land and allows cold, moist air, plus winds and fog to move into the area.

During the 1990s, the Sonoma County wine

Sonoma County wine

Sonoma County wine is wine made in Sonoma County, California, USA. County names in the United States automatically qualify as legal appellations of origin for wine produced from grapes grown in that county and do not require registration with the United States Department of the Treasury, Alcohol...

 industry adopted the term Petaluma Gap to help differentiate its products. The gap is a part of the Sonoma Coast AVA

Sonoma Coast AVA

The Sonoma Coast AVA is an American Viticultural Area in Sonoma County, California, USA containing more than , mostly along the coastline of the Pacific Ocean. It extends from San Pablo Bay to the border with Mendocino County. The appellation is known for its cool climate and high rainfall...

, a designated American Viticultural Area

American Viticultural Area

An American Viticultural Area is a designated wine grape-growing region in the United States distinguishable by geographic features, with boundaries defined by the Alcohol and Tobacco Tax and Trade Bureau , United States Department of the Treasury....

, but is not itself an AVA. Wine grapes growing in the Petaluma Gap are said to be influenced enough by this climate to give the area's wines a distinctive character. The wind-driven cool moisture reduces heat stress on grapevines, allowing the production of wines that require exacting temperatures and humidities for proper fruiting. In 2006, twenty-four local organizations and individuals formed a promotional group called the Petaluma Gap Grape and Wine Alliance.