Marin open space ranger Carl Szawarzenski faces a seemingly Herculean task: carving a new 5-foot-wide path out of a steep slope high above Lucas Valley in San Rafael as part of the county’s new 680 Trail.

The slope is filled with rock, brush and dirt, and Szawarzenski must navigate a narrow ledge; one false move could send him tumbling down the hillside.

But with a few handy tools — including a mini bulldozer — he adeptly snakes his way through the rough to create a multi-use trail that will used by thousands in the coming years.

“It’s very challenging as you can see, but it’s enjoyable,” he said.

Typically he can get in the mini bulldozer and push through hundreds of pounds of soil and tree roots to create a new pathway along the slopes that have been made dusty and dry by the summer sun.

“It usually goes easily, but then you run into something like this,” said Szawarzenski, as he clanged a shovel head against a slab of bedrock that his dozer will not be able to get through. Worse yet, it’s on a bend, meaning he will not be able to simply go around it.

The solution: a jackhammer.

“Usually it breaks up. Rock in Marin is pretty soft, but not this piece,” Szawarzenski said. “The trail will be great once we buff it all out.”

But for now it’s a work in progress, the county’s latest addition to its myriad hiking, biking and equestrian trails.

The new trail was born from controversy.

In 2008, Marin rocker James Hetfield of Metallica erected a metal fence, tired of people trashing his land. The fence effectively cut off the popular Luiz Ranch Fire Trail that linked the Terra Linda-Sleepy Hollow Divide and Loma Alta open space preserves.

The solution was a new trail that would work its way around the Hetfield land. The rocker has been accommodating to the work, allowing crews to use his road for better access. He also improved the road, said Chris Bramham, superintendent of capital projects for the Marin Open Space District.

“The access makes it easier for us to build the trail,” Bramham said, as he gave a tour of the work-in-progress trail last week. “And he paid for the road improvements, too. We have no complaints with him.”

The 680 Trail — named for its peak elevation of 680 feet above sea level — could get a more official name once the path is done, which could be as soon as Sept. 15. It could then open by the spring. If work can’t be completely wrapped up by Oct. 15, it will be finished next summer. Work began May 16.

Cost for the trail included about $620,000 from the county and a $56,000 grant from the North Bay Conservation Corps. The high cost was driven by environmental reviews, trail design, materials and equipment, as well as technical reports needed to comply with state environmental rules so permits could be issued.

In addition to the new trail, existing fire roads as well as parts of the Solstice and Meditation trails have been closed and are being re-tooled to form the new 680 Trail. When it’s all finished, hikers, bikers and equestrians will enjoy expansive views of the bay, valleys and rolling hills that surround the trail.

“When it’s done it will be beautiful,” Bramham said, pausing to look over the bay. “The views from here are fantastic.”

But before then, there is plenty of work to do for open space workers, Conservation Corps North Bay employees and a cadre of volunteers along the roughly three-mile trail that will be about 5 feet wide.

Eight wooden bridges are being built over drainages, the small valleys where water comes down and crosses the pathway. Some of the drainage areas have been transformed into mini-construction sites where wood, concrete, electricity and people power are used to build the bridges.

“This is our third bridge here,” said open space maintenance equipment operator Dave Frazier as he and his crew worked on a 12-foot span, pouring footings and cutting planks. “We are getting there.”

Durable pressure-treated wood — material that has been treated with a preservative — is used for the floor of the bridge, while redwood is the choice for the rails. Thick, wooden recycled railroad ties are used as a base.

“The bridge has to look nice, but it has to be durable and be able to handle the weight of a vehicle,” Bramham said, adding that drainages that are shallower will have rock crossings that users can step across.

Bramham — a veteran of trail-building efforts in the county — said the path construction has been difficult at times.

“It’s one of the more technically challenging trails we have done because of the slopes and the varying terrain and soils,” he said. “We have stopped work because of bird nesting, stormwater pollution issues and rain events.”

Great care has been taken not to upset wildlife during work and special reports were done before construction started so as not to disturb badgers, birds, bats and red-legged frogs.

“We have seen some rattlesnakes around, so you have to be careful when rocks are moved,” Bramham. “I guess we are working in their home turf.”

Contact Mark Prado via email at mprado@marinij.com

680 Trail at a glance

Âo Length: 2.9 miles

Âo Cost: In excess of $650,000

Âo Connects: Terra Linda-Sleepy Hollow Divide and the Loma Alta open space preserves.

Âo The need: Bypasses a trail closed by Metallica rock star James Hetfield

Âo When open: Spring 2012 if work is finished by October or sooner