Scenes of a stretch of property along state hiway 90 between I-10 and Karchner Caverns State Park, the proposed future home of 28000-home development Villages at Vigneto in Benson.

Ron Medvescek / Arizona Daily Star / File

Federal officials have suspended a crucial permit for a 28,000-home development planned in Benson, to the relief of opponents who fear the project will dry up the San Pedro River and harm federally protected wildlife that depend on it.

In a July 20 letter to Villages at Vigneto's developer, a U.S. Army Corps of Engineers official said the suspension was "in the public interest" while consultation is pending regarding the project's potential to affect protected species and their habitats.

"The suspension is effective immediately," said the letter, which the Star obtained Thursday. "Upon receipt of this correspondence, you are ordered to stop those activities previously authorized by the suspended permit." The permit, which applies to 8,200 acres of the 12,000-acre development, allowed the developer to fill desert washes on 51 acres in order to construct the project.

Mike Reinbold of developer El Dorado Benson LLC, a subsidiary of Phoenix-based El Dorado Holdings, has not yet responded to the Star's request for comment.

The move comes just days after Benson's City Council unanimously approved a final master plan for the project, which envisions a golf course, vineyards, schools, lakes, medical facilities and commercial and office space.

Environmentalists have argued the approval was premature, without resolution to concerns about whether the project's federal Clean Water Act permit — which the Corps issued in 2006 to an earlier developer — was still valid.

Last year, the U.S. Fish and Wildlife Service asked the Corps to begin consultation on the Vigneto's potential impacts, which could result in the permit being rescinded. The service said consultation should evaluate impacts to two federally protected species, the Western yellow-billed cuckoo and Northern Mexican garter snake, which have been newly listed since the permit was issued 10 years ago. The service also said since Vigneto is 50 percent bigger than its predecessor, Whetstone Ranch, the Corps should reevaluate the project's potential to affect the endangered jaguar and the lesser long-nosed bat.

Conservationists have taken the argument to the courts. In May, six environmental groups filed a lawsuit, arguing Section 7 of the Endangered Species Act requires federal agencies to consult with the wildlife service before issuing a permit for a private construction project that may affect an endangered species.

It's not clear whether formal consultation has been formally initiated yet, but the Corps' move to suspend the permit is a positive step, Chris Eaton, Earthjustice associate attorney, said on Thursday.

"The Corps’ good-faith action to put Vigneto’s development on hold while the Corps and (wildlife service) determine what additional environmental reviews and conditions are necessary is good news for the San Pedro River, and the communities and wildlife that rely on it," Eaton said in an email. "This does not resolve our lawsuit, but is a step forward."

Officials from the Corps and the Fish and Wildlife Service have not yet responded to the Star's questions about the pending consultation.

Contact reporter Emily Bregel at ebregel@tucson.com or 573-4233. On Twitter: @EmilyBregel