A genus of pathogenic fungi with two species, Coccidiodes immitis and C. posadasii. C. immitis and C. posadasii are thermally dimorphic fungi found in soil particularly in warm and dry areas with low rainfall, high summer temperatures, and low altitude. The two species are morphologically identical but genetically and epidemiologically distinct. C. immitis is geographically limited to California's San Joaquin valley region, whereas C. posadasii is found in the desert southwest of the U.S., Mexico, and South America. The two species appear to co-exist in the desert southwest and Mexico. Both cause coccidioidomycosis.