You're probably right about California. Even with the Spanish missions, not everything dates back to the period when the missions were active--some were destroyed by earthquakes or fell into decay after secularization and had to be rebuilt, but in most cases there are probably parts of the original structures around. I once visited Mission San Antonio and found a painted potsherd on the ground, presumably decorated by one of the Indians during mission days.
Santa Clara University has Old Mission Santa Clara on its campus but I think it is a smaller replica built later. It has the grave of Peter Hardeman Burnett, the first American governor of California (who was a convert to Catholicism).
I was thinking about that nut case who sues the state over religion. (He has none), Get him on the stand and ask him to give us the English name of several cities.