Carex xerophila Janeway & Zika is described from gabbro and serpentine soils on the west slope of the northern Sierra Nevada in California. It is documented from four populations in or on the margins of chaparral and open forest. The new species is assigned to Carex section Acrocystis Dumort., and a key is provided for all California representatives of the section. Carex xerophila differs from C. globosa Boott in its uniformly short, erect basal peduncles and Sierra foothills habitats. Carex xerophila differs from C. brainerdii Mack. by its green leaves that are not densely papillose below, its relatively shorter perigynium beaks, and its lower elevation montane habitats. Carex xerophila has more strongly nerved scales and perigynium faces than C. rossii Boott.