In 1938, two botanists, Elzada Clover and Lois Jotter, made an ambitious voyage down the Colorado River driven by the desire to chronicle the plant life of the American Southwest. In her new book Brave the Wild River, science journalist Melissa Sevigny traces their expedition through the Grand Canyon, which led them through seething rapids and the occasional mishap. Journalists of the day gawked at their gender and the pair were forced to pick up chores labeled as “women’s work." Still, they managed to collect hundreds of plants that hadn't yet been catalogued by researchers. Their observations about desert ecosystems...