I was born and raised in Los Angeles, where the oldest thing was San Fernando Mission back from 1797. *THE OLDEST*.
I think I can find buildings older than that just up the street from here...
Goodness, I rather assumed there would be some buildings from the 1600s in California (and possibly structures from pre-European civilisations) but apparently not! Not only do structures not come from then but there was no occupation by Europe in the 1600s really.... huh!