One of the most scenic spots in Marin has just become more accessible for visitors as part of an $850,000 upgrade.

A project has launched to improve a trail on the back side of Hawk Hill, the scenic spot high in the Marin Headlands that is a gathering place for bird watchers.

National Park Service trail crews have realigned the existing Hawk Hill Trail, constructed railings and lowered the grade of the path to make it more accessible to users. A steep staircase and eroded trail had made it hard for some people to use, officials said.

“It’s beautiful,” said Amity Gregg, of San Francisco, who was running the new trail Monday morning, as she stopped to look over the new route. “They did a great job.”

The new alignment resulted in a grade of less than 8 percent and offers an easier way to get to the top of Hawk Hill by accessing a tunnel below the site.

In all, about 1,000 feet of trail will be reworked. Additional phases will be worked on next year. The Golden Gate National Parks Conservancy will lead efforts to revegetate the landscape with 7,500 native plants following construction.

The 900-foot-high Hawk Hill offers panoramic vistas of the Golden Gate Bridge, San Francisco and Rodeo Beach.

Kirsten Holder, project manager for the Golden Gate National Recreation Area, was pleased with the first phase of work that wrapped up recently.

“That staircase is now gone and we now have more of a winding trail that makes access easier,” she said. “We also wanted to cut down on the number of social trails, which better protects the habitat.”

The site’s name is connected to its pre-eminence as one of the best places in the state to view and monitor 19 raptor species.

On virtually every day between mid-August and early December, a group of volunteers gathers to count hawks, eagles, falcons and other birds of prey as they glide by.

Built into the hill is Battery Construction 129. A World War II-era structure, it had two large guns mounted under thick concrete shields that were covered with native vegetation for camouflage, according to the park service. It features tunnels that connect the two gun pits, magazines and storage rooms. The site was never put to battle and was designated for public use.

The trail work is the latest project at the site. In 2011, the park service removed a grove of about 200 non-native trees to help create more habitat for the endangered mission blue butterfly.

The removal of the trees was part of “Project Headlands,” an $8.7 million federal effort to improve access for motorists, bicyclists, pedestrians and public transit in the Marin Headlands. As part of that work, the National Park Service had to mitigate the impact of its roadwork — such as finding ways to improve wildlife habitat.

One step the agency took was to cut down the trees in order to plant lupine that will create mission blue butterfly habitat.

The forest was relatively new and did not exist before 1970 beyond a handful of trees, because the military kept the trees in check to avoid a visual impairment that might block views of the ocean.

It was not known exactly how the trees arrived. One theory is that they came with soil brought from nearby Kirby Cove to cover concrete bunkers built into the hillside by the military. Pines were planted in Kirby Cove in the early part of the 20th century and the soil might have had seeds in it.

The new trail configuration agreed with Joe Zawadzki, who came from Folsom with his daughter to take in the sweeping views on the bright, clear day.

“It’s always so beautiful here,” he said with a smile as he looked out over the Golden Gate.