Mallory and her brother are surprised when Kate, a cousin they barely know, joins their family vacation. With Kate reading aloud "Fun Facts" about the Grand Canyon, the long road trip seems interminable, but after riding mules into the canyon and whitewater rafting down the Colorado River, the kids become friends as well as kin. Written in journal format and illustrated with cartoonlike grayscale drawings, this chapter book has an accessible look. The story arc may be predictable, but fans of the long-running Mallory series will enjoy reading about this soon-to-be fifth-grader, her initially unbearable cousin, and her sometimes inscrutable older brother.