Cirsium perplexans is a species of flowering plant in the aster family known by the common names Rocky Mountain thistle and Adobe Hills thistle. It is endemic to Colorado in the United States, where it occurs in the Colorado and Gunnison River Valleys in the Rocky Mountains.This species is a biennial herb growing up to one meter tall from a taproot. The stems are coated thinly in webby fibers. The leaves are up to 30 centimeters long by 6 wide.