Calochortus umpquaensis is a species of flowering plant in the lily family known by the common name Umpqua mariposa lily. It is endemic to Oregon in the United States, where it is mainly limited to the region of the Klamath Mountains on the Little River in Douglas County, in particular the Watson and Ace Williams Mountains. The flower has also been found at a single location in each of Josephine and Jackson Counties. Though rare in general, the plant can be locally abundant, with the population at Ace Williams Mountain containing 400,000 to 800,000 individuals.