LAST SUMMER while driving home to Texas after participating in the first annual Artistic Horizons show in Bozeman, MT, Denise LaRue Mahlke swung through Yellowstone National Park. “One of the things that grabbed me there were the geyser pools,” she recalls. “They were infatuating to me. It was magical how they all looked so different. Some were like mud pots in opaque greens or reds. Others were clear, giant pools that looked incredibly deep and almost iridescent in shades of emerald and sapphire. One reminded me of a peacock feather. I could have stood and stared at them for hours,...