The spiral trace fossil Gyrolithes de Saporta, 1884 in the Pliocene Tirabuzon Formation near Santa Rosalia, Baja California Sur, Mexico, by Edward C. Wilson. Bull. Southern California Acad. Sci., 84(2):57-66, 1985. The largest recorded specimens of the enigmatic spiral trace fossil Gyrolithes are abundant in the Pliocene Tirabuzon Formation near Santa Rosalia, Baja California Sur, Mexico. They grade gradually into Thalassinoides-type burrows. Both types of burrows are lined by scratch marks, suggesting excavation by a decapod crustacean. Associated mollusks indicate a depth of 55 to 90 m.