DUBLIN -- The fate of a rural canyon that is home to ranching families has become a key issue in the race for two City Council seats in this fast growing city.

Debate over Doolan Canyon, which lies between Dublin and Livermore, is getting livelier as candidates for City Council weigh in on whether to preserve the grasslands or allow a 1,990-home retirement community to be built there.

Six candidates are running for two seats.

One City Council candidate says she wants Dublin to adopt an urban growth boundary on its fast growing east side near Livermore.

"I'm opposed to this continuous urban sprawl," said Anita Carr, a Council candidate who favors the limits. "We've had too much sprawl. I'm concerned about the impacts if we had 2,000 more homes east of Dublin."

Mayor Tim Sbranti, who is running unopposed, agrees. Carr and other City Council candidates say it's too early, though, to say how much of the sparsely populated land between the two cities should be declared off limits to development.

Some of the area already is preserved. In 2010, the East Bay Regional Park District paid $6.4 million to buy 640 acres -- a square mile of Doolan Canyon land -- to form the core of a new regional park to provide hiking areas and to protect habitat for species like the threatened California red-legged frog.

The park district also has begun land purchase negotiations to buy adjacent land to the north in Contra Costa County.

The Sierra Club and Greenbelt Alliance say all of the Alameda County land between the two cities should be protected to protect wildlife habitat, ease traffic congestion and pollution ills, and provide motivation and energy for Dublin to revitalize its downtown.

Likewise, Save Mount Diablo is encouraging land in the area to be preserved.

"It's a legacy issue whether we have sprawl clogging our roads or preservation protecting our quality of life," said Matt Vander Sluis, the East Bay senior field representative for Greenbelt Alliance. "It's clear to us this is one of the biggest environmental issues facing the Tri-Valley area."

Candidates agree the future of the area in and around Doolan Canyon is important.

But several say it's premature to declare the entire area between the two cities off limits to major development, especially while Dublin and Livermore are holding talks about planning control of the area.

Those talks are aimed at diffusing tension between the cities after the Dublin City Council in 2010 authorized a study on whether to add to its sphere of influence some 1,450 acres where Danville-based Pacific Union Homes has proposed to build the retirement community.

Only a few ranch houses are now located in the area, and the water wells are unreliable there, officials say.

"I do not want to rush to a decision," said Councilman Kevin Hart, an incumbent running for re-election. "I would agree there should be a requirement for some open space and some boundary for development, but I am not willing to shut it down in the area."

After all, Hart said, "We're not talking about building an oil refinery, We're talking about a housing center on par with Rossmoor in Walnut Creek."

David Haubert, a Dublin School Board member running for the Council, said he thinks it would be premature for Dublin to adopt a new growth boundary limit barring development in all the area between the two cities.

Haubert said that while some of the land should be protected, "I don't know that the Doolan Canyon area is another Yosemite."

Doreen Wehrenberg, a Dublin planning commissioner also running for the Council, agrees it's premature to decide the area's future without an environmental impact report on how development would affect the area.

Two other Council candidates -- Shawn Costello and Shehu Hassan -- said they want open space preservation east of Dublin but couldn't say how much.

Mayor Tim Sbranti said Dublin should set an urban limit line for eastern Dublin, as it did for western Dublin in 2000. But where to draw the line is still to be determined, he said

"As the city gets closer to built out," he said, "it gets more important to see where your limits are going to be."

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff