Some weekend to-do lists are ambitious.

Others can be downright intimidating.

Such as:

• Build a 24-foot-long bridge.

• Install and build a trail over a 12-foot-long culvert.

• Clear a cluttered steam.

• Build a levee of logs to prevent a stream from eroding a trail during periods of high water.

• Cut and fill several sections of a trail to make it more user-friendly for mountain bikers and pick-your-speed pedestrians.

• Close off two poorly designed trails so they can return to nature.

And do it all in less than three hours.

All you need are multi-talented people, tools with the appearance of medieval weaponry, experience, energy, enthusiasm -- and a leader with a plan.

"We couldn't have done it without the help of everyone here," said Barry Jeffries.

When Mr. Jeffries arrived at Pack pavilion in Boyce Park on Aug. 3, for his first day as a trail steward, he hoped about 35 volunteers would show up to help improve one of the park's multi-use trails. He was delighted when 51 men, women and teenagers from the Pittsburgh Trails Advocacy Group, PTAG, showed up from all over Allegheny County.

Mr. Jeffries welcomed everyone and asked them to sign in, complete a liability waiver form required by the county and pick up raffle tickets for some bike-related giveaways afterward.

Mr. Jeffries, who lives in Penn Township, owns and operates Dirty Harry's, a popular full-service bike shop in Verona. He's been riding a bike for 40 of his 47 years and has been a member of Pittsburgh Trails since 2001, when it was spun off from Pittsburgh Off Road Cyclists.

As a trail steward, he was responsible for organizing the day's activities that included equal amounts of trail work, mountain biking and picnicking.

Pittsburgh Trails, whose motto is "Better Trails Through Stewardship," works hard and plays hard.

Dave Biber, of Bellevue, a co-founder of the advocacy group, quickly got the attention of everyone, especially newcomers, when he talked about the "circle of death." That's the area that surrounds volunteers when they use large tools, especially a McLeod or a Pulaski.

A McLeod is a long-handled tool. It has a four large teeth on one end for raking and a sharp edge on the opposite end that can cut roots, brush and dirt. It also can be used to tamp dirt.

A Pulaski can be used as an ax and a small hoe. It cuts through underbrush and dirt with ease.

The county, which approves all PTGA trail projects, loans tools to the group to make those tasks easier. If a project requires power tools, county employees do that work.

Mr. Biber, 46, is a self-described "mouse jockey" at Carnegie Mellon University, where he is designer/illustrator. He reminded the volunteers to wear gloves, pace themselves, take breaks and keep themselves hydrated.

Although the early-morning temperature was 60 degrees, the forecast called for sunshine with a high of 81 degrees.

The group leaders led volunteers from the pavilion to the work sites, about a mile into the woods. They walked a short distance down a road, passed the archery range and continued single- and double-file along the trail. The surface was muddy in spots, covered with surface coal in places, and curved past a tower supporting electric wires.

Then they got right to work.

Joshua Carson, 34, of Lower Burrell, and Scott Root, 53, of Fox Chapel, went to work on the log levee with several others.

Eric Steadle, 40, of Penn Hills, and his wife, Nancy, 37, entered the stream to clear it of tree limbs that had come down in storms.

Jim Snyder, 43, of Penn Hills, and his sister, Janet, 41, were joined by Caryn Csuy, 46, of Churchill, in widening and leveling a section of the trail.

John O'Toole and Brian Miller and others installed the black plastic culvert, covered it with dirt, tamped it down with McLeods and bordered it with logs to hold the trail in place.

They used short logs to erect a strainer to prevent debris from clogging the culvert from the runoff of a storm.

Scott Gray, 41, of North Huntingdon, and a crew that included Mr. Jeffries, Darren McInnis, Jack Gruendel, Chris Beech, Brian Miller and Cory Shugats worked on the bridge site.

"Anybody who rides here knows this was the biggest mudhole, probably from forever," said Bob Bannon, of Plum, as he looked at the mud under the bridge.

Completing the bridge was a challenge.

The four rails for the bridge and several dozen pieces of decking, all cut to size, had been delivered earlier that week. Two of the rails and 15 pieces of decking disappeared a few days later.

Mr. Jeffries thought he was going to have to replace all of that. But Pittsburgh Trails volunteer Julie Gaul spotted the items in a nearby section of woods while running on a trail. They were quickly recovered and carried one-quarter mile down to the work site.

Mr. Jeffries, however, did have to drive to a home improvement store to buy more concrete block to support the bridge. Wheelbarrows, which earlier had been used to transport hundreds of pounds of flat rocks to stabilize the approaches to and from the bridge and cover soft spots, carried the block to the bridge.

After completing their tasks in less than three hours, the volunteers returned to the pavilion. They got on their bikes and, depending on their ability level, followed trail leaders into the park. They returned several hours later for a picnic.

PTGA, a project of Bike Pittsburgh, was founded in 2001 by Mr. Biber, Nancy Trun, Danielle Conway and Don Olson "to protect and encourage shared use trail access in Western Pennsylvania."

It works with public and private landowners to make sure trail projects meet standards set by the International Mountain Bicycling Association, "with minimal impact on the environment."

"I'm really proud of PTAG," said county Parks Director Andrew Baechle, who also is a mountain biker. "They do work no one else wants to do, and they do it with a smile."

Years ago, relations were strained among the trail users -- mountain bikers, equestrians and those who used the trails for walking or running.

"We got everyone together in the same room and talked about what we wanted to do," Mr. Baechle said. "Each group was told they would have a voice in how things were done. I said mountain biking is a perfectly proper leisure activity, and that today's mountain bikers are yesterday's horsemen."

Mr. Baechle praised Don Schmitt, a regional recreation supervisor based in North Park, for his efforts "in making this all work."

"I can't say enough good things about him. He was on vacation when the Boyce Park trail work was to be done. He drove in to make sure the PTAG volunteers had the tools they needed."

For more information, go to ptagtrails.com.