Also called Yellow-spine Thistle, and having a fatal resemblance to the invasive Carduus nutans, or Nodding Thistle, this native has a rough go. It is also colonized by the insect imported to control C.Nutans. Note the fuzzy leaves which are a soft sage green, and the white stripes on the bracts. Flowers which appear to have been torn apart probably contain a "Bumble Flower Beetle" (Euphoria inda), a scarab beetle who loves nectar.
In this photo notice the different shapes of the involucres, or vase-like parts below the flowers. They also show different numbers of bracts. These distracting features are confusing. It is the length of the corolla lobes (13mm) that made me ID these as C.ochrocentrum rather than C.undulatum, plus the fact that C.undulatum lives on the eastern plains, and C. ochrocentrum lives at higher elevations. Regarding "Cirsium," Weber himself says,"This genus is very poorly understood in the Rocky Mountains, and the key has to remain very tentative."