PHOENIX -- The Arizona Diamondbacks and Colorado Rockies are NL West rivals. Now they're partners in a spring training facility planned for the Salt River Pima-Maricopa Indian Community near Phoenix.

Under an agreement announced Thursday, the tribe will build an 11,000-seat ballpark and a complex that includes 12 practice fields, training facilities and offices. The facility is expected to be ready for the 2011 exhibition season.

The 140-acre site is adjacent to Scottsdale. It is believed to be the first major league spring training facility on tribal land.

"We are certainly excited that we have come to an agreement on our future spring training home with a wonderful community," Diamondbacks president and CEO Derrick Hall said. "We have had several interested parties and sites but ultimately found this site to be superb."

The Diamondbacks have held spring training operations at Tucson Electric Park since the team's inception in 1998, sharing the facility with the Chicago White Sox until 2008.

The White Sox moved into a new facility with the Los Angeles Dodgers near the Phoenix-Glendale border last year, leaving only the Diamondbacks and Rockies in Tucson.

With most Cactus League teams in the Phoenix area, the Diamondbacks and Rockies said it was inconvenient to travel to road games. The Diamondbacks also wanted to be closer to their fan base.

The Rockies trained at Tucson's aging Hi Corbett Field since their inception in 1993.

"We know that this shared home will be one of the finest year-round training facilities in all of Major League Baseball and something that our organizations, fans and the community will be proud of for decades to come," Rockies president Keli McGregor said.

The deal announced Thursday is for 25 years with options to extend the term.

The tribe and the clubs said they would make joint decisions on the design of the facility near Indian Bend Road and the Loop 101 freeway, a short distance from a casino operated by the tribe and an adjacent large hotel that is under construction. HKS Architects, which recently designed the Camelback Ranch-Glendale facility for the Dodgers and White Sox, is designing the new facility.

"Our ancestors built ball courts on this land and throughout the valley," said Diane Enos, president of the Salt River Pima-Maricopa Indian Community. "Now we are excited about bringing baseball home to our community."