Populus angustifolia, commonly known as the narrowleaf cottonwood, is a species of tree in the willow family (Salicaceae). It is native to western North America, where it is a characteristic species of the Rocky Mountains and the surrounding plains. It ranges north to the provinces of Alberta and Saskatchewan in Canada and south to the states of Chihuahua, Coahuila, and Sonora in Mexico. Its natural habitat is by streams and creeks between 3,900 to 7,900 feet (1,200 to 2,400 m) elevation.

The tree is slim in profile, and can grow in tightly packed clusters. Its leaves are yellow-green, lanceolate (lance-shaped), and with scalloped margins. It produces catkins in the early spring. The fruiting capsules are fluffy and white.

Source
Wikipedia