The last time this taxon was featured on BPotD, I used the name Cirsium peckii. I was unaware that a 2004 publication had reclassified a number of thistle species into varieties of Cirsium eatonii, including another thistle featured on BPotD, Cirsium clokeyi — now Cirsium eatonii var. clokeyi. The rationale from the Flora of North America entry on Cirsium eatonii linked above: “Several of the races recognized here as varieties have been treated in the past as species (e.g., Cirsium clokeyi, Cirsium peckii). Their current geographic isolation and more or less distinctive features might support such recognition, but application of this approach across the complex would result in a proliferation of microspecies.” In other words, split it into many species or lump them all together: a classic problem for those who try to categorize the diversity of life into tidy little boxes. Groups undergoing speciation at an observable scale defy tidy little boxes.
Leaving aside the issue of names, Steens Mountain thistle is found only in southeast Oregon on Steens Mountain and the nearby Pueblo Mountains (I’ve only seen it on Steens so far) and northeast Nevada. This is quite a robust thistle, growing to 150cm. Of the taxa featured in this regional endemic series, it is probably the least threatened; it is a common plant at higher elevations on Steens Mountain, growing in a number of habitats — including the disturbed roadside gravel. My two trips to Steens have occurred in early July, so I suspect I’ve never seen peak bloom of Cirsium eatonii var. peckii (mid- to late July would be best, I think).