For whatever reason — maybe because of the way the mountains stand out crisply and firmly against the sky — hard-edge abstraction has deep roots in Colorado, going back more than half a century to the work of Aspen's Herbert Bayer. Other artists in the state who have embraced the approach include Angelo de Benedetto, Otto Bach, Bev Rosen, George Woodman, Clark Richert and David Yust. And straight lines and sharp edges still have their fans, as evidenced by the work of Pard Morrison, a leader in the current generation of Colorado artists who could be called hard-edged abstractionists. At the Edge of the World, his show at Rule Gallery when it was still located on Broadway (it's relocating to RiNo this spring) represented something of a breakthrough for Morrison, with his checkerboard paintings turning into checkerboard sculptures. Based on the sumptuous works in this show, that was clearly the best move that Morrison could have made.