Centaurea maculosa Lam.
A biennial or short lived perennial with a large taproot; 1 to 3 ft tall.  Principal stem leaves are pinnately divided.  Flowering heads have stiff bracts tipped with a dark fringe.  Flowers are usually pinkish-purple.

Introduced from Eurasia as a contaminant in alfalfa and clover seed.  
It establishes quickly on disturbed ground and appears to inhibit the growth of surrounding vegetatation.

Western Montana is heavily infested.

Photos and information adapted from "Weeds of the West" by Tom Whitson