Natural Bridges Day Use Area is an awesome geological place on Cayote Creek, off Parrots Ferry Road (on the North side of the Parrots Ferry Bridge over the Stanislaus River). It is unlike anything you'll ever see. There are signs to show the way.
We hiked the mile to the stream with friends where we sat at a picnic table next to the water. The gaping cave mouth is a little intimidating but I got right in the ice cold water and swam approximately 90 yards through to the other side of the "natural bridge". What an experience!
The entrance presents the appearance of a noble Gothic arch of massive stone-work, thirty-two feet in height above the water, and twenty-five feet in width at the abutments; the rock and earth above, supported by the arch, are thirty or more feet in thickness, and overgrown with trees and shrubbery.
We were there early in the day and only saw a family from France come by our way. I understand there is another "bridge" downstream equally as amazing, but didn't venture there that day.