Clark explored the Yellowstone River in a boat made of lashed cottonwood trees. These trees, which grow along many plains rivers, proved invaluable throughout the journey, providing shade and shelter as well as transportation. To commemorate the tree, Clark named the site where he constructed the boats Camp Cottonwood. But the massive groves have been dying out because of dams, which block the seasonal flooding of the riverbanks. Cottonwoods, both this species and black cottonwood, Populus trichocarpa, which occurs further west, require the rich silt deposited by high springtime water in order to germinate. Since dams have altered the rivers' flow, no new trees are taking root to replace the old ones. Along the Garrison Reach of the Missouri River, the Sierra Club is planting cottonwoods and working to restore the river to its natural flow patterns.

Black cottonwood (subspecies) is state threatened.