Activity above ground by the white desertsnail, Eremarionta immaculata, in relation to air temperature and humidity (saturation deficit) was observed during daylight 2 to 5 days following rainfall of 12 mm on 11 January 2001. A maximum of 12 snails was observed active within a 15-m by 15-m quadrat near the type locality of the species in the Riverside Mountains, California. Number of active snails increased as air temperature (8 to 23°C) increased and as saturation deficit (2.5 to 16 mm Hg) decreased. Most variation in number of active snails was attributed to saturation deficit. Active snails preferred epiphyta (lichen and moss) as a substrate compared with other types of substrate (plant detritus and 4 size-classes of rocks) within the quadrat. Epiphyta might provide active snails with food or with a moister surface, increasing water absorption.