If you aren't riding a mountain bike with a sturdy frame and fat tires, you probably shouldn't attempt the final four miles of the Butler-Freeport Trail. Or, you should go on foot.

"It is open," said Chris Ziegler, president of the Butler-Freeport Community Trail Council. "But it is rough."

The all-volunteer group took part in a ground breaking for the project this month. "We wanted people to be aware of this part of the trail," she said. "Riders should check it out."

The final section runs from the Summit municipal building on Bonniebrook Road, northwest through Summit and Butler townships. Crossing the Connoquenessing Creek via an old railroad bridge, the trail ends near the city of Butler's Father Marinaro Park.

The biking and hiking path is being built on the right of way of what originally was called the Western Pennsylvania Railroad. It later became the Butler branch of the Pennsylvania Railroad.

Trail council work parties have been cutting brush and doing preliminary grading to get the trail ready for its top coat of crushed limestone.

While the present surface alternates between mud and rock, which makes it rough going for cyclists, the route remains a monument to the skill of the 19th century surveyors who brought rail service to Butler.

Herman Road, which often runs parallel to the former rail line, twists, turns, rises and falls on its route north between Summit and Butler. The trail, on the other hand, has long straight stretches with a slight grade and gentle curves. That meant railroad builders had to carve shelves into the sides of hills, fill in gullies and cut through mounds of rock.

Planning for the rails-to-trail project began 20 years ago, and organizers had to overcome strong opposition in many communities before construction could begin.

The trail starts at Freeport and passes through Buffalo, Winfield, Jefferson, Summit, Butler Township and the city of Butler.

For its first 12 miles, it follows the valley carved by the Buffalo and the Little Buffalo Creeks. The route is often shaded by trees as it crosses and recrosses the streams.

Beyond the village of Marwood in Winfield, the landscape opens up, and the trail passes by farm fields, pastures and poultry barns. Riders are warned to stop for golf carts as the trail divides the Serene Valley Golf Course.

At the village of Herman in Summit, a new display board describes the history of the railroad and the village that grew up around it.

Beyond Herman, the trail passes behind the Summit Township Sportsmen's Club. Large signs warn "Caution: Rifle Range next 3/4 mile." The shooting range is parallel to the trail, Ms. Ziegler said. While trail users don't have to worry about stray bullets, they shouldn't be surprised to hear gunfire, she said.

The landscape becomes more industrial along the trail's final two miles. Its route takes riders behind factories and warehouses that developed along the rail line as it approached Butler. The trail ends near the north bank of the Connoquenessing Creek.

Although it passes through many communities, the trail is owned by Buffalo Township. It is maintained with the help of local municipalities, adjoining landowners and the trail council.

Buffalo supervisors are awaiting word on their application for a $250,000 state grant to help pay for materials to complete the last section of the trail. Trail supporters hope to finish the project early next year.

On a recent Sunday afternoon, the southern portion of the trail was busy, drawing dog walkers, bicycle riders and joggers.

"They keep it in really good condition," said Rick Keeler, of Jefferson. "And there are new benches and picnic tables."

He, his wife Johnna and their son Garrett, 8, try to get out on the trail at least once a week.

Mr. Keeler uses a motorized wheelchair, and he was pleased to find that the trial near his home is handicapped-accessible.

"You meet a lot of nice people out here," he said.