President Barack Obama will designate a portion of the San Gabriel Mountains as a national monument on Friday during a ceremony at Bonelli Park in San Dimas, the White House announced Wednesday.

President Obama will give a speech at Frank G. Bonelli Park to formally announce the designation at 1 p.m, said Rep. Judy Chu, D-Pasadena, who has been working on giving the mountains federal recognition for several years as a way to increase funding for trails, safety and maintenance.

“I am overjoyed and thrilled,” Chu said Wednesday after getting a phone call from the White House. “This is an historic moment. It is the biggest change to the San Gabriel Mountains since 1908.”

San Dimas City Councilman Denis Bertone, a supporter of the proposal, said he has learned the president would be using Brackett Field Airport in La Verne, most likely as a place to land his helicopter, Marine One.

The president will arrive in Los Angeles Thursday afternoon to attend a town hall at Cross Campus, a business start-up incubator in Santa Monica, before leaving for a Democratic National Committee fundraiser in the evening at the Los Angeles home of Academy-Award winning actor Gwyneth Paltrow.

“We heard he will be landing in Brackett Field,” Bertone said. Brackett Field airport is located adjacent to Bonelli Park, a 1,975-acre county regional park with a view of the San Gabriel Mountains.

The president will board Air Force One at LAX at 2:20 p.m. Friday and fly to San Francisco, according to an itinerary released by the White House.

The proposal for a national monument came out of a bill by Chu, and before that, by then-Rep. Hilda Solis to declare the mountains, San Gabriel and Rio Hondo rivers and Puente Hills a national recreation area. But when her bill was stymied in Congress, she asked the White House to step in.

However, a national monument can only include federal land and will not take in the rivers, nor Puente Hills because that is private and/or county land.

Presidents have the power to designate wilderness and historical resources as national monuments under the Antiquities Act of 1906. So far, President Obama has designated 12 national monuments, the last one was the Organ Mountains-Desert Peaks National Monument in south-central New Mexico in May.

The proposed San Gabriel Mountains National Monument would stretch from Castaic to the San Bernardino County border but will not include Mt. Baldy, Wrightwood or Cucamonga Canyon. These areas, part of the San Bernardino National Forest, were removed from the designation proposal after the San Bernardino County Board of Supervisors objected.

Supervisor Janice Rutherford said San Bernardino county residents were bypassed. “There have been discussions for years and years in the San Gabriel Valley. There has not been a single public hearing on this in San Bernardino County,” Rutherford said Wednesday in a telephone interview.

What was once configured from Castaic to I-15 and about 532,000 acres has shrunk to 346,000 acres of the mountain range and only in the Angeles National Forest, Chu said. She said the Obama administration removed that portion from the monument. “They took their feedback seriously,” she said.

Many groups, including The Wilderness Society, San Gabriel Mountains Forever, Council of Mexican Federations or COFEM, the Asian Pacific Policy and Planning Council, Bike SGV, the San Gabriel Valley Water Association, the San Gabriel Valley Council of Governments are supportive of the both Chu’s bill and the presidential action.

Chu said the proposal for a national monument would bring added recognition to the area, which is visited by 3 million people a year. The area can receive more resources for rangers, trail maintenance and signs if designated as a national monument.

“I believe it will make a huge difference with regards to all the problems in the San Gabriel Mountains,” Chu said. “I’ve talked to the (Obama) Administration and they have assured me there will be more resources for the San Gabriel Mountains.”

One area she’d like to see improved is safety. At Eaton Canyon above Pasadena, five hikers have fallen to their deaths in recent years. “We will put in much better safety measures in these kinds of areas,” Chu said.

Those who argued that recreational opportunities would be curtailed under monument designation are mistaken, she said. “The most important thing is it includes a greater ability to enjoy recreation from hiking, fishing, hunting to all things previously allowed.”

Yet, Los Angeles County Supervisor Michael Antonovich said the county has concerns about how a national monument designation will affect firefighting, flood control, water resources and roads. “Congresswoman Chu and the president are bypassing stakeholders by rushing this monument designation,” he said in a prepared statement released Wednesday. Antonovich said the designation should be put off until various county agencies sign off.

Rosemead Councilwoman Margaret Clark said she disagreed with the monument proposal and the use of a presidential declaration. “This is bypassing the democratic process. The idea that if you don’t like a bill you can have it done by fiat? I don’t think so.”

Staff writers James Steinberg and Neil Nisperos contributed to this article.