Construction of the South Mountain Freeway could begin next month after a federal court in Phoenix dismissed legal challenges.
The U.S. District Court ruled Friday the Arizona Department of Transportation and Federal Highway Administration completed all steps required to move forward.
But the Gila River Indian Community and a coalition of environmental and community groups say they'll appeal to the 9th U.S. Circuit Court of Appeals.
The tribe says South Mountain is considered a sacred and cultural resource.
"The path of this freeway will destroy parts of South Mountain that for centuries have been among the Community's most important and sacred natural resources," said Gila River Gov. Stephen Lewis in a statement. "This freeway will wipe out or significantly alter trails, shrines, and archaeological sites that are significant cultural resources for the Community and our members.
ADOT officials say the 22-mile freeway is expected to open by late 2019 and connect Interstate 10 in Chandler and Laveen.
"This is a clear victory for the region, which will benefit from a new transportation corridor and, with it, the economic development that will follow," ADOT Director John Halikowski said in a news release.
Approved by Maricopa County voters in 1985 and 2004 as part of a comprehensive regional transportation plan, the South Mountain Freeway will complete the Loop 202 and Loop 101 system.