"They needed to get gravel back in the woods -- in places their equipment couldn't go," Knowlton said. "Me and my buddy sat down and put some ideas together."
In the end, their horse-drawn contraption -- fabricated from scratch with little more than scrap metal -- proved to be a resounding success, said Glen Kansanback, a natural resource specialist in Sumter National Forest's Long Cane district.
"The main thrust was that we needed to put gravel out on our horse trails that were getting mucky from being wet," Kansanback said. "They aren't accessible from our Forest Service access roads."
A second problem, he said, was to find a way to spread the gravel along the narrow trails without heavy equipment.
Kansanback and a colleague, Libby Meadows, explored using mules equipped with hard panyards -- reinforced saddlebags -- to haul the gravel, which would then be spread by hand.
Knowlton and Wetzel weren't fond of the panyard idea and decided to come up with their own.
"We used the back axle from under a minivan -- and a whole bunch of scrap metal," said Knowlton, a welder who also ran a machine shop for 30 years. "Whatever we didn't have, we made."
Their final product was a horse-drawn gravel-hauling cart that could carry a ton of aggregate. It also had a tapered box with a gate that could be opened slowly, allowing the gravel to self-spread as the horses moved forward.
"In a little more than a day's time, we spread right at 60 tons of rock," Kansanback said. "It's a very different piece of equipment."
The Forest Service now uses the device whenever it needs to maintain remote trails, and Wetzel and Knowlton provide the horses.
"It was fun to build," Knowlton said. "And it actually worked better than I thought it would."