Pima County will buy 615 acres of land west of Interstate 10 for about $4.2 million for recreation, flood control and transportation projects.

The Board of Supervisors approved the purchase Tuesday.

"In the years to come, this is going to be something that defines a portion of this board's legacy," said Supervisor Richard Elías. "It's such a huge effort to use that land in a different way than it's ever been used before."

CalPortland owns the land and mines it for sand and gravel. The land is west of Interstate 10 between Orange Grove and Curtis roads.

Over 20 years or so, the county plans to install bank protection on the Santa Cruz River, develop a lake for water recharge, build soccer fields and other recreation facilities, and build a road through the property that would extend Sunset Road from River to Silverbell roads. It's part of a project called Corazón de los Tres Ríos del Norte (Heart of the Three Northern Rivers).

The county Flood Control District is buying the land because of its proximity to the Santa Cruz and Rillito rivers, but the county still must identify other funds to turn it into a park.

In 2010, the Pima County Bond Advisory Committee recommended asking voters to approve $10 million for the Corazón project at the next county bond election, which has yet to be scheduled.

The northernmost portion of the land, which is in Marana, could be redeveloped as a retail shopping center after CalPortland relocates its operations.

In other action, the Board of Supervisors unanimously passed a resolution of support for the existing and future missions of Davis-Monthan Air Force Base and the Arizona Air National Guard's 162nd Fighter Wing - including a potential F-35 training mission.

"I wanted to make it very clear - not only to other jurisdictions in our region but very clear to our congressional leadership as well as leadership in the Pentagon - that this community, its leadership and its elected officials do adamantly support D-M and the 162nd and their missions," said board chair Ramón Valadez.

Rep. Ron Barber, D-Ariz., and the Tucson Metro Chamber were among those offering their support at the meeting Tuesday.

Contact reporter Becky Pallack at bpallack@azstarnet.com or 573-4346. On Twitter @BeckyPallack.