In the summer of 1938, botanists Elzada Clover and Lois Jotter set off down the Colorado River, accompanied by an ambitious expedition leader and three amateur boatmen. With its churning rapids, sheer cliffs and boat-shattering boulders, the Colorado River was famed as the most dangerous river in the world. But for Clover and Jotter, it held a tantalising appeal: no one had surveyed the Grand Canyon's plants, and they were determined to be the first.

Through the vibrant letters and diaries of the two women, science journalist Melissa L. Sevigny traces their forty-three-day journey, during which they ran rapids, chased a runaway boat and turned their harshest critic into an ally. Their story is a spell-binding adventure of two women who risked their lives to make an unprecedented botanical survey of a little-known corner of the American West at a time when human influences had begun to change it forever.