The Mount Lyell salamander (Hydromantes platycephalus) is a species of salamander in the family Plethodontidae. It is endemic to the Sierra Nevada of California, United States. It is found in a range of microhabitats, such as rock exposures, talus and rock fissures, and under rocks or in caves or crevices. Its altitudinal range is 1220m–3670mm (4,000feet–12,040feetm) above sea level. No significant threats to this species are known.