San Benito mountain, Mountain summit in Diablo Range, California

San Benito Mountain is the highest summit of the Diablo Range, reaching 5,267 feet (1,605 m) in San Benito County. Its rock is chrysotile serpentine, an ultramafic stone that weathers into nutrient-poor soils high in magnesium and heavy metals. These soils support little vegetation but harbor endemic plants such as the San Benito evening primrose, and a pine and incense cedar forest grows at the highest elevations.

The mountain's serpentine mass was mined for chrysotile asbestos at the Atlas Asbestos Mine and Johns-Mansville, both now Superfund sites. Cinnabar, chromite, magnesite and jadeite were also extracted, and the Gem Mine within the mass is the only source of gem-grade benitoite in the world. The Clear Creek Serpentine Area of Critical Environmental Concern was withdrawn from mineral entry on August 7, 2012.

The San Benito Mountain Research Natural Area protects a collection of rare plant species adapted to the mountain's serpentine soil conditions.

Access to certain areas requires special permits due to naturally occurring asbestos in the soil and rock. Visitors should check regulations before planning a visit and follow all guidance provided by local authorities.

The serpentine rock formations create unusual soil conditions that support plant species found nowhere else, adapted specifically to the mineral-rich environment. These rare plant communities are now protected as part of a research natural area.