A new decapod fauna has been recovered from Eocene rocks of San Diego County, California. Decapod faunas of Eocene age have been rare from California, although they are well described from the northern Pacific coast. Three new species, including Neocallichirus rhinos, Ctenocheles secretanae, and Minohellenus inexpressus, and two new genera and species, Acanthoportunus buchanani and Vegarthron santiago, are reported from this new fauna. A new genus has been erected to accommodate Portunites triangulum and Portunites granulifer; both are herein referred to Maeandricampus, new genus. Callianassa matsoni Rathbun has been reassigned to Neocallichirus. Portions of the cephalothorax and abdomen of a species of Ctenocheles are described from fossils for the first time. Orbitoplax weaveri, previously known from Eocene rocks of California and Oregon, is reported from the Eocene Mission Valley Formation and the Ardath Shale for the first time. In addition, one specimen of a stomatopod of indeterminate genus is noted. The Eocene decapod fauna from California, now containing eighteen genera, has elements common to the northern Pacific coast of North America as well as taxa known only from California; thus, the area appears to have been suited for decapods adapted to a wide variety of temperature and other environmental conditions. Several genera appear to have evolved within the region, whereas others may have been introduced from the Atlantic or Tethys region via the Central American Seaway. The number of Pacific amphitropical genera continues to increase; two portunid genera discussed here display such a pattern, adding to the four already reported for Cretaceous and Tertiary rocks of the region.