Nearly 9,000 acres in Sonoma County and almost 22,000 acres in Mendocino County were designated Tuesday as critical habitat for the threatened California red-legged frog.

The land is part of 1.6 million acres in 27 counties that the U.S. Fish & Wildlife Service has dedicated as necessary for the frog's survival.

The rules specifically give ranchers immunity from the Endangered Species Act for routine ranching operations, said Al Donner, a spokesman for Fish & Wildlife Service.

However, converting ranch land to vineyards or non-agricultural uses would require permission of the federal agency.

The decision, said Donner, will help protect "a lot of the most important habitat for the species."

Tuesday marked the third time that federal officials have designated critical habitat for the frog. The first attempt in 2001 was set aside after legal action by the construction industry. The second in 2006 was put to rest at least in part because of litigation by environmentalists charging political interference by the Bush administration.

The new rules for the first time designate land in Mendocino County as critical habitat. The 21,800-acre area lies north of Point Arena near Manchester and includes much of the Mills Creek watershed.

Sonoma County has three areas deemed critical habitat: about 1,500 acres of Annadel State Park; nearly 5,000 acres east of Petaluma in the Sonoma Mountains; and 2,200 acres southwest of Petaluma near West Petaluma Regional Park.

An environmental group that sued for a new designation called Tuesday's rules a "substantial improvement" from those of the Bush administration.

"It gives the frog a chance of recovery," said Noah Greenwald, the endangered species program director in Portland for the Center for Biological Diversity.

The red-legged frog, said Greenwald, was made famous in the Mark Twain story "The Celebrated Jumping Frog of Calaveras County."

"At one time this would have been the most abundant frog in California," he said. But the loss of wetlands and pollution of waterways has decreased the frog's historic habitat by 70 percent.