Walnut Canyon National Monument, in northern Arizona, was named for its population of Arizona walnut (Juglans major). To increase knowledge of the species' population size and status, the National Park Service conducted a census in 2011–2012 of all Arizona walnut trees in the monument and evaluated their characteristics. The monument contained 2,065 Arizona walnut trees. All size classes were well represented, from seedlings (<1.4 m tall) to mature trees over 15 m tall. The largest individuals had a diameter (at 1.4 m) of 103 cm and a height of 23 m. Over 80% of trees exhibited at least medium vigor (>50% live crown), indicating that trees were healthy across size classes.