Farming on hillsides and high elevations is a tricky business, but winemakers have been harvesting grapes from the slopes of Moon Mountain in the Mayacmas range for generations.

Now, after more than a decade of attempts, the grape growers and wineries that farm on the mountain's slopes have been approved for a new American Viticultural Area.

The new "Moon Mountain District Sonoma County" east of Highway 12 spans 17,663 acres and includes 1,500 acres of commercial vineyards planted at elevations from 400 to 2,200 feet.

The designation, which was approved by federal regulators at the Alcohol and Tobacco Tax and Trade Bureau, allows vintners to describe the origin of their wines on the label while giving consumers information to identify where a wine comes from.

The new appellation is located within the Sonoma Valley AVA, but the mountain vintners have long wanted to differentiate their wines on the labels.

"Because it was part of Sonoma Valley, it's been hard to get any story about mountain-grown wines and how they're special," said Christian Borcher, co-founder of Repris Wines, who pushed for the designation. "Wines that are grown on the hills and the top of the mountain are distinctly different and usually a higher quality than what you can grow on the valley floor."

Hillside vines produce smaller berries, so there's more skin to impart flavor on the juice from the grapes, Borcher said.

More than 40 vineyards and 11 bonded wineries grow grapes in the region. Some of the oldest cabernet sauvignon and pinot noir vines in the state are grown in the Moon Mountain region, Borcher said. The Monte Rosso Vineyard, originally planted in the late 1800s, is among the historic vineyards located in the new AVA.

The new AVA is the 16th in Sonoma County and the fourth located within the Sonoma Valley AVA.

"Adding another AVA will help us just clarify those different microclimates and little growing regions within the major Sonoma Valley," said Maureen Cottingham, executive director of the Sonoma Valley Vintners & Growers Alliance.

Mountainside farming is more expensive and painstaking than developing vineyards on the valley floor, said Erich Bradley, winemaker at Repris Wines.

"There's not a lot of organic matter that's naturally found in the soils up here," Bradley said. "That translates into control for the farmer or the winemaker. The wines only get the water and the nutrients that we give them, and that is a huge advantage, because we can be more consistent with our product."

The Sonoma Mountain appellation, also in Sonoma Valley, has more variability in its terrain and is cooler than the Moon Mountain AVA, Bradley said.

Randall Watkins, winemaker at Watkins Family Winery, made an attempt to carve out an AVA more than a decade ago, but the growers and wineries didn't agree on a name, he said.

"We're pretty excited about it," Bradley said. "It's been a long time coming."