Lower Pliocene petrified wood from the Palm Spring Formation, Anza Borrego Desert State Park, California

This investigation identifies the abundant petrified wood found in the basal Diablo Member of the Palm Spring Formation, Anza Borrego Desert State Park. Three families of temperate hardwood trees are recognized from the fossil wood cell structure. The Lauraceae represented by Umbellularia , the Salicaceae with specimens of Populus and Salix , and the Juglandaceae represented by Juglans . A review of the paleontologic and paleomagnetic literature establishes the base of the Diablo Member at approximately 3.8 m.y.B.P. with continued deposition for 1.2 m.y. The unique paleobotanical assemblage found in the Diablo Member together with the floral ecology of present-day equivalents reflects a temperate climate with ocean influence and predominantly winter rainfall in this region during the Lower Pliocene Epoch.