Bad weeds. Bad, bad weeds.

Chris Biggs of Tampa, Fla., stood in a Dumpster at 909 Saint John St., and tromped on the wayward green things with a periodic stab with a shovel.

"I'm teaching these weeds a lesson - not to grow at this house anymore," Biggs said.

He and 31 cyclists with the Bike & Build program's Providence, R.I.-to-Seattle route arrived in Casper on Friday and stayed Saturday to help the Heart of Wyoming Habitat for Humanity chapter complete two houses at Saint John and H streets.

Bike & Build organizes cross-country bicycle trips which benefit affordable groups such as Habitat for Humanity that provide housing for needy families willing to put in their own sweat equity to build their homes. Since its founding in 2003, Bike & Build has raised more than $1.6 million and its cyclists have pedaled more than 3.1 million miles.

Saturday marked the 45th of the 68-day trip, with 2,503 miles of the 3,874-mile trip completed. Their stop in Casper marked the sixth of eight "build days."

Biggs - a 2007 University of Florida graduate who spent a year teaching English in South Korea - heard about Bike & Build from a friend who cycled from Providence to San Francisco, he said. "She said when she was done she had withdrawal symptoms."

While he was stomping those pesky weeds, others were preparing the yard for sod, mixing concrete for posts for a chain-link fence, and doing interior trim work.

"I like the variety," he said.

Raj Bhandari, a graduate of the University of Pennsylvania, took off the summer for the ride before entering Stanford University in a decision sciences engineering program.

Bhandari doesn't mind getting his hands dirty, he said. "Yard work is fun; we were done weeding in an hour."

As they've been climbing from sea level, some of the bikers have had to adjust to the elevation of the Rocky Mountain Region, said Isabel Gottlieb of Seattle. "You get used to it pretty fast."

Some of the pain has been eased by major sponsor Giant, which donated its Defy 2 model to each participant, she said.

The bikers get used to each other, too, Biggs said. "I don't think I've ever been this busy, learning leadership and teamwork."

The 32 bikers are divided into four groups, each with a leader.

Group leader Susanna Bee of Portland, Ore., said the volunteers range in age from 18 to 27 and they include college students and graduates, Bee said. "Some quit their jobs and will figure out what to do."

Bee graduated from Willamette University in Salem, Ore., and took a three-month leave from her nonprofit organization Children's Healing Art Project, she said.

Building affordable housing cuts to the heart of many social problems, Bee said. "Having a home provides so many things for a family - a sense of security, safety and community; things that are (unknown) in substandard housing."

While some of the volunteers in the Providence-Seattle group knew each other, most did not before their trip, she said.

The volunteers are required to each raise $4,000, Bee said. "This group, we've raised over $150,000."

She raised money through writing letters to friends asking for donations, hosting parties, and holding art auctions, she said.

One volunteer set up a training bike on a street corner in a city, rode on it all day, and people tossed money in a basket, Bee said.

Some of what they raise is applied to expenses, but most is used for donations to affordable housing agencies through Bike & Build, the hosts in the towns where they build, and through the biker's individual choice, she said.

Bee is in charge of arranging the logistics of the route including shelter and food, she said.

In Casper, Hometown Buffet provided free dinner Saturday, and the Best Western Ramkota Hotel donated rooms, she said. "We usually stay on church basement floors," Bee said. "We have not slept in beds in a long time; it was a big treat."

Bee and the 31 others started in Providence with a two-day orientation including a day working on a housing project before hitting the road.

The bikers - accompanied by a support vehicle carrying their gear - headed west through Connecticut, New York, Pennsylvania, Ohio, Indiana, Illinois, Iowa, South Dakota, Nebraska, and entered Wyoming at Lusk on Wednesday.

They biked through Lusk and Douglas, and arrived in Casper on Friday.

Today, they head for Shoshoni, Lander, Dubois and Jackson, and enter Idaho on Thursday. From there they bike through Montana and again in Idaho, and finish in Washington.

"The most touching thing we've come across is the generosity of the towns we've been in - food, shelter, or even just a warm welcome," Bee said.

Reach Tom Morton at (307) 266-0592, or at tom.morton@trib.com. Read his blog at tribtown.trib.com/TomMorton/blog.