Mycena californiensis is a species of fungus in the Mycenaceae family. It is a common and abundant species in the coastal oak woodlands of California, where it grows saprobically, feeding on the fallen leaves and acorns of various oak species. First described in 1860 by Berkeley and Curtis, the species was collected four years earlier during an exploring and surveying expedition. It was subsequently considered a doubtful species by later Mycena researchers, until a 1999 publication validated the taxon. Mycena elegantula is considered a synonym.