Four years ago, Will Montague and Matt Giaraffa watched as carbon-fiber mountain bikes—which are both strong and light—became the latest rage. From their vantage point at Guerrilla Gravity, their small bike shop in Jefferson Park, they saw two problems with the sport’s newest trend: At the time, most companies outsourced the labor-intensive production to Asia, and the few that did assemble the parts stateside charged dearly for it, selling frames for $3,000 to $5,000. Montague and Giaraffa decided they could learn how to produce made-in-the-USA models for less than major brands. First, they found a tougher carbon-fiber composite used in airplanes. Then, Giaraffa, who has a mechanical engineering background, spent three years tinkering with manufacturing techniques and ultimately came up with a process that involves more automation and 80 percent less physical labor. The result? Riders can hit one of the many resort bike parks that open in Colorado this month on a Guerrilla Gravity product that’s around $1,000 cheaper (frames start at $2,195) and 300 percent more impact-resistant than other carbon-fiber creations.