Extensive hydrothermal alteration is visible in valley walls of a thermal area near the summit of Cerro Evermann. Steam rises from fumaroles in this 1998 view. The largest fumarolic vent is located at the head of a large barranca NE of the summit. During a 1957 visit by Mooser and Bryan, temperatures of 65-97° C were measured. Similar temperatures ranging from 61-101° C were measured in 1993.

Photo by Martha Marin, 1998 (Mexican Navy).

Socorro