Jon S. Galehouse Warren O. Addicott 1973 <p>Marine invertebrates from the Paso Robles Formation&nbsp;recently discovered near Atascadero, Calif., indicate that the basal part&nbsp;of this chiefly nonmarine deposit is of provincial early Pliocene age.&nbsp;Heretofore the lack of direct fossil or radiometric evidence of the age of&nbsp;the Paso Robles has made it a difficult unit to place in the late&nbsp;Cenozoic history of the Coast Ranges. The assemblage is dominated by&nbsp;<i>Ostrea vespertina</i> and by <i>Nettastomella rostrata</i>, a rock-boring bivalve;&nbsp;its mode of preservation indicates that the fossils are in place and have<br />not been recycled from older marine formations. This occurrence&nbsp;suggests that during the early Pliocene a seaway connected the present<br />southern Salinas Valley area with the northern part of the Santa Maria&nbsp;basin; the fossils occur about halfway between the southernmost<br />exposures of the Pancho Rico Formation near San Miguel and&nbsp;fossiliferous strata east of Pismo Beach, both marine units of early&nbsp;Pliocene age.</p> application/pdf en U.S. Geological Survey Pliocene marine fossils in the Paso Robles Formation, California article