Justin Burd of Set in Stone, a craft concrete business, mixes concrete for the bases the handmade trophies the company is making for the River Rocks outdoor competition at their building on Thursday in Chattanooga, Tenn.

They sat untouched in the Ocoee River for thousands of years. But next month, they'll be trophies.

Twenty-four victors of Chattanooga's RiverRocks adventure sports games, from Wednesday through Oct. 13, will hoist newly designed awards made from river rocks. Concrete casters at Main Street's Set in Stone have been shaping the natural trophies into highly coveted prizes.

The mantel mementos are the brainchild of shop owner Nathan Smith and Dave Santucci of the Chattanooga Area Convention and Visitors Bureau.

"It's great when you can integrate natural elements found in nature into a trophy," Smith said. "We do a lot of things here just for the fun of it."

The shop -- which takes on anything from kitchen countertops to 7-foot-tall chess-inspired columns -- hummed Thursday afternoon as workers ground and polished the heavy, yet handheld, awards.

As the afternoon sun peeked through the dust-ridden workspace, Staj Olsen chipped away at the stones with a tile saw while Justin Burd poured a sloppy concrete mix into a base mold.

Eventually, the stone halves and concrete bases would be joined in a three-day assembly process.

"We take them outside, polish them and make them perfect," Burd said.

Burd insists the most difficult part of the slow-going process is the very beginning: etching the reusable mold by hand, ensuring details of the revamped logo and motif show up in the final products.

"It's such a small mold, we actually have to carve this logo out and then make a reverse mold," he said.

Although Set in Stone is more accustomed to designing tables and benches, this isn't the shop's first try at trophies. They designed the awards for last year's "Swim the Suck" 10-mile race through the Tennessee River Gorge.

The grand prize? A pearl-white, teardrop-shaped concrete sculpture smoothed so fine it could be mistaken for porcelain. The voluptuous shape was inspired by "diving into water," and could only be shaped with a plastic mold.

The solid concrete result was elegant, but not perfect.

"We had about four that didn't work out," Olsen said. "We just made a few extras and picked the ones that ended up looking best."

How the RiverRocks awards will be distributed remains to be determined in some of the 12 events.

For example, the Sequatchie Valley Century 100-mile bike race is a "noncompetitive event," so organizers are considering using the awards to celebrate the oldest and youngest finishers of the grueling ride.

"Last year, we had a 18-year old take 16 hours to finish the race," Santucci said. "We were waiting there at midnight. How great would it be to give them an award?"

Contact staff writer Jeff LaFave at jlafave@timesfreepress.com or 423-757-6592.