Our family calls this the Idaho Saguaro - because it resembles the saguaro (cactus) of Arizona and Mexico. See a real one here. The "Idaho Saguaro" is a common roadside weed. This one was found along the road near the Boise River. It could be an important exotic or native plant? It's not on the state "noxious weeds" list. Maybe someone checking this blog can identify it. On a side note, there is a subdivision in the suburbs called "Saguaro Canyon" - which is funny because the true saguaro can't possibly grow here. And we noticed that the cactus plants they did install quickly died.