Calochortus tiburonensis, the Tiburon Mariposa Lily, is a rare member of the genus Calochortus in the family Liliaceae. It is endemic to Marin County, California, where it is known only from one population on Ring Mountain east of Mill Valley. There it occurs on a single serpentine outcrop in grasslands from 50–150 metres (160–490 ft) in elevation. Calflora taxon report, University of California @ Berkeley: Calochortus tiburonensis Tiburon mariposa lily