ARLINGTON — Walk onto the old railroad trestle north of town and you’ll see the Stillaguamish River at a dizzying distance below.

Anybody brave enough to venture too far would run into a sign: “This corridor is closed to all public use.”

Before too long, this sign could turn into a welcome mat.

Work is expected to begin today to extend the Centennial Trail, Snohomish County parks’ most popular attraction, by 8 miles north from the trestle. By early next year, this path to the Skagit County line could open a window to rural landscapes, and a new portal for tourism in Arlington.

“This next portion, it’s just really different. It’s more rural, more wild country,” said Beth Hill, a horse-riding enthusiast from Marysville and the Centennial Trail Coalition’s incoming chairwoman. “You’re very much riding through woods and woody hillsides. It’s just got a different feel to it.”

The first 6-mile section between Snohomish and Lake Stevens opened in 1989, Washington’s centennial.

Now, the trail goes from Snohomish north of Marsyville with few interruptions. The only major gap in the 17-mile run to Arlington is a mile or so where it spills onto 67th Avenue NE, a two-lane county road.

The new section costing $4.9 million should be done by early 2011. It will follow a rail corridor dating from the late 19th century.

One person looking forward to riding it is George Boulton, the retired former owner of Flowers by George in Arlington’s downtown. The 73-year-old and his wife already are avid cyclers on southern portions of the trail.

“We can’t wait to get out of church on Sundays and ride down to Snohomish and back on our bicycles,” he said.

Boulton and other trail supporters also view the trail as an economic driver. They hope it brings more delis, cafes and perhaps a bicycle shop and a hotel to downtown Arlington.

About 350,000 people per year use the trail by Lake Stevens, said Bea Randall, the current trail coalition chairwoman and one of the project’s original supporters.

“If that many people use the trail in Arlington, it’ll really be a big tourism boost,” she said.

An added attraction that Randall and others are promoting is lining the railroad trestle over the Stilly with flowers and hanging vines. The idea is patterned after the Bridge of Flowers in Shelburne Falls, Mass. That would liven up the current construction plans, which call for concrete decking and guardrails over the trestle’s sturdy railroad timbers.

The company doing the next phase of the trail also did previous sections. Strider Construction of Bellingham bid nearly $4.9 million, which was far less than engineers’ original estimate of $6 million.

From downtown Arlington, the new trail will cross the trestle over the Stillaguamish River, then head to the Bryant community, where a future trailhead is planned.

From there, it would pass over Pilchuck Creek with a new steel bridge and head through the privately owned Pilchuck Tree Farm, popular with horseback riders and mountain bikers.

When the work is finished, trail users will have an almost unbroken 50-mile round trip from end to end. Still, one significant problem will remain: the Arlington gap.

After 152nd Street NE, the trail peters out, forcing trail users onto 67th Avenue NE. About a mile later, the path picks up at 172nd Street NE on sidewalks that lead to Arlington.

That would be the next priority after the trail reaches the Skagit County line, Snohomish County parks director Tom Teigen said.

Another related project is the Whitehorse Trail, which links with the Centennial Trail just over the trestle from downtown Arlington. Whitehorse, another former rail line, would be 27 miles long with 18 bridge crossings. The plan is to build it gradually into a contiguous gravel trail up to Darrington, starting with a section from near the trestle to Cloverdale.

“It’s not going to be paved for years — we’re talking huge costs,” Teigen said. “You’re not going to roller blade on it, and you’re not going to take your street touring bike on it.”

Noah Haglund: 425-339-3465, nhaglund@heraldnet.com.