Rep. Adam Schiff came out in opposition on Thursday to a proposed alignment of the state’s high-speed rail project that would require a tunnel beneath the Angeles National Forest – damaging chances the plan will be carried out.

In a letter sent this month, Schiff, D-Burbank, and Rep. Judy Chu, D-El Monte, told California High Speed Rail Authority Dan Richard to scrap any consideration of a route under the San Gabriel Mountains between Palmdale and the San Fernando Valley because it would be harmful to the environment.

Los Angeles County Supervisor Michael Antonovich suggested to the authority last summer that it look at all conceivable routes including an alignment that would go through the mountains and national forest.

Such an alignment, he said, could decrease travel times and mute opposition that may arise in the unincorporated neighborhoods where the original alignment would pass as trains traveled between stations in Palmdale and Burbank largely following Highway 15 and the 5 Freeway.

“Any benefits gained by going through the forest do not outweigh the far greater costs to the project and the damage that might be done to our environment,” Schiff and Chu said in the letter.

Additionally, the letter said, the route could add delays to the project because the San Gabriel Mountains were designated a national monument last year by President Obama and the U.S. Forest Service is now drawing up a management plan for the forest.

“California needs high-speed rail – but it needs to be done in the right way, with proper thought given to how a particular route will affect communities and the environment,” Schiff said in a prepared statement.

Antonovich spokesman Tony Bell said the supervisor supports whichever rail alignment is best for the communities it will pass through. “He merely said do not go with one over the other but to study them all. We do not propose one (route) over the other,” he said.

The rail authority is currently studying an alignment between Palmdale and Burbank with a decision expected to be made this spring.

The authority’s original proposal was for a 45-mile section between Palmdale and Burbank roughly following the 14 freeway to where it meets the 5 freeway in Santa Clarita. From there it would pick up existing tracks parallel to San Fernando Road south to Burbank. Parts of that route would require about 20 miles of tunnel in sections through the mountains, near the interchange of the 14 and 5 freeways, the Sand Canyon area, and between the unincorporated communities of Agua Dulce and Acton.

The option floated by Antonovich would instead have the trains leave Palmdale east of the 14 freeway, traveling in a 15- to 20-mile tunnel burrowed deep under the San Gabriel Mountains and the Angeles National Forest, and exit near neighborhoods in the east San Fernando Valley, perhaps Pacoima, Lake View Terrace or Sun Valley.

An exact alignment on where it would enter and exit the mountains has yet to be developed but the plan has already drawn bitter opposition from the neighborhoods where the tunnel might exit.

The ambitious $68 billion high-speed rail project would connect Los Angeles and San Francisco by 2029. A groundbreaking was held last week for the first 29-mile segment between Fresno and Madera in the Central Valley.

That segment is part of a larger first phase that would end in Burbank and cost nearly $28 billion. The authority wants to finish the phase by 2022 and projects 10.4 million riders within three years of opening, but that figure has been derided by critics of the project.