Calochortus tiburonensis is a perennial lily that is an edaphic endemic of serpentine grasslands on a single summit on the Tiburon Peninsula in Marin County, California, U.S.A. The single population is located within the Ring Mountain Preserve. Recreational activities and non-native plants are the primary threats to this species. This species relies on ongoing active management to control the spread of non-native plants that can outcompete the lily. This species meets the requirements for Critically Endangered under criterion B for area (EOO <100 km², AOO <10 km²), a continuing decline in the quality of habitat, and number of locations (1).

Calochortus tiburonensis is endemic to California, U.S.A., where it is endemic to Ring Mountain of the Tiburon Peninsula, on the northwestern side of San Francisco Bay in Marin County. There is a single occurrence of nine colonies that occupy different patches of exposed serpentine (USFWS 2019).

In 1991, it was estimated that in the one known population there were 40,000 individuals (USFWS 1995).

This species occurs in serpentine grasslands (serpentine bunchgrass community), primarily on open, rocky slopes (USFWS 2011, 2019).

The primary threats to this species are recreational activities and non-native plants. Potential overuse of the preserve due to its proximity to residential communities, and specifically by, bicycling, motorbikes, and pedestrians is a risk to the plant, primarily through off trail use and expansion of unofficial side trails (USFWS 1995, 2011). Non-native plant species, that can outcompete and displace the lily, will likely need ongoing removal to keep their presence under control. Due to the species' rarity, random events such as fire, disease outbreak, landslides, or vandalism could have catastrophic effects on this species. Herbivory by Mule Deer (Odocoileus hemionus) and Black-tailed Jackrabbits (Lepus californicus) is a minor threat (USFWS 2011).

This species occurs in the Ring Mountain Preserve. It is Threatened in the state of California and Threatened under the U.S. Endangered Species Act.