The general consensus is that this natural bridge was formed by normal erosion caused by years of ocean wave action. That notion is incorrect. Evidently, at one time, like more than 200 years ago, the polar ice caps were so massive, there was no ocean in this area.
At that time, there were two Yokut native brothers named Ibbig and Ibbigger who loved to play croquet. The boys were huge, you know, from eating all natural foods and abstaining from alcohol, tobacco, sex and rock n' roll. Being big boys, they played with big balls and needed a wicket large enough for the balls. Pileated Woodpeckers were rather large at that time in history, so, the boys grabbed a couple of birds in each hand and directed their incessant hammering tendencies on the rock. The birds did this because, after all, the boys had big balls and you don't mess with boys with big balls.
(everything above is a fabrication, just so you know)
Natural Bridges State Park, Santa Cruz, California 2014