From WNPS:
Black Cottonwood is a tall, upright, deciduous, widely-distributed tree which grows along stream banks, along riparian corridors, moist forests, and other wet areas.
 
The winter buds are yellowish-brown, very pointed, and covered in a resinous substance which smells similar to balsam. This is a fast-growing tree which can reach 50 feet (15 m) in only 10 years.
 
Black cottonwoods are very fast growing and are easy to propagate with stem cuttings. The root systems help stabilize the soil, which is especially important for the restoration and conservation of riparian (river) areas they are commonly found growing in. Black cottonwoods have a high nitrate uptake.
 
Primary photo credit: Daniel Mayer (mav) on Wikimedia Commons (CC BY-SA 3.0 Deed)
Secondary photo credit: NatureShutterbug on Flickr (CC BY 2.0 Deed)