It is found in California, Oregon, Washington, Idaho, Montana, Nevada, and Utah.

[4] Ageratina occidentalis is a rhizomatous perennial herb growing fuzzy green or purple stems to a maximum height near 70 centimeters.

The inflorescence is a dense cluster of fuzzy flower heads containing long, protruding disc florets in shades of white, pink, and blue.

[5] Ageratina is derived from Greek meaning 'un-aging', in reference to the flowers keeping their color for a long time.

[6] The name Eupatorium comes from the Greek king Mithridates VI Eupator, who is said to have discovered that a species in the genus could be used as an antidote to a common poison.