The Irvine Co. will offer 2,500 acres of undeveloped land in Anaheim Hills and near East Orange that was once to hold 5,500 homes to the county today, in hopes of ensuring the massive swath remains open space forever, company officials said.

Documents of the proposal, which have been kept quiet, will be privately handed over to the Board of Supervisors concerning what likely would be the landholder’s last big gift of open space. The panel is not scheduled to discuss the proposal during today’s meeting.

“As we celebrate the 150th anniversary of the Irvine Co., this is the perfect opportunity to add to our open space and park lands legacy,” Irvine Co. Chairman Donald Bren said in a statement. “With this gift, we complete our open-space vision.”

If the county accepts the donated land – there could be costs to maintaining it – 55,000 acres of the Irvine Ranch’s original 93,000 acres will be a protected, natural landscape.

“We are most grateful for the Irvine Co.’s 20,000-acre donation in 2010 and try to be the best stewards of the land we can be,” said Supervisor John Moorlach, referring to a gift that included 2,000 acres of wilderness in Black Starr Canyon.

“If they want to make another offer, we’ll do the same for the benefit of our current and future residents,” the supervisor said.

The land gift could add a large swath of preserved space on the northern parts of the Irvine Ranch, joining other protected natural terrain in the stretches of Weir Canyon, Fremont Canyon, Black Starr Canyon, Limestone Canyon, Irvine Lake and Irvine Regional Park.

Protected areas of the ranch land are used by more than two million outdoor enthusiasts each year, Irvine Co. officials said. People hike, bike, run and ride horseback on the ranch lands. The latest gift, like the others, would offer docent-led tours and nature classes.

In Anaheim Hills, 2,500 homes could be built on the 1,100 acres of rolling hills, oak woodlands, rocky parts and native grasslands among canyons. The land, within the city of Anaheim, is bordered on the north by the 91 and is alongside the Eastern Toll Road.

The city approved the homes in 1991, with some residents in Anaheim Hills and Yorba Linda worried about traffic impacts. The recession slowed down the project from moving forward; the city-approved development agreement allows the Irvine Co. to begin construction any time before October 2030.

“I think it will be a beautiful recreation area for residents in Anaheim and the county,” said Anaheim Councilwoman Kris Murray, who lives in Anaheim Hills.

In the East Orange area, a plan was approved allowing 3,000 homes on hills including ridge lines and meadows. The 1,400 acres are east of the 241 and alongside the southeastern shore of Irvine Lake.

The land slated for this development is outside of city limits, but if developed, the city would have annexed the land, City Manager John Sibley said. If preserved, Orange will not pursue the annexation.

Orange Mayor Tita Smith said the city didn’t oppose the homes but appreciates the Irvine Co.’s effort to preserve open space.

“In Orange, we highly value open space even if it’s adjacent to the city because we think it’s an important facet of life in Orange,” she said.

If the county accepts the land, the preservation of 60 percent of the Irvine Ranch land as open space far exceeds an original 11 percent planned by developers in the 1960s, said Daniel Young, president of the Irvine Co.

It could take months for the supervisors to reach a decision on the land.

“While we know homes in Anaheim Hills and East Orange would resonate with homebuyers, we also realize that preserved open space will enhance and help complete the network of trails in that area,” Young said.

Esmael Adibi, an economist at Chapman University, applauded the Irvine Co.’s offer.

“One of the things we get criticized for is that we’re getting too crowded and there’s too much traffic,“ he said of Orange County. “The Irvine Co. is large enough that 5,500 homes, relatively speaking, is not important.

“If the supply of homes is restricted that also supports existing home prices,” Adibi said. “In the end, it’s a business decision. They have to decide, ‘Do we build homes or dedicate land, which is more important?’”

Staff writers Rebecca Kheel and Art Marroquin contributed to this report.

Contact the writer: 949-492-5152 or eritchie@ocregister.com or twitter.com/lagunaini