I love old stuff....but growing up in Kalifornia, the oldest man-made object I’ve ever touched would probably be a couple of the coastal Mission buildings.
:’)
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).
You haven’t looked very hard. I found a lot of Indian artifacts, including spear points, flint shaping tools and arrowheads in the California desert and Sierra Nevada mountains. A lot of petroglyphs dating back thousands of years on the 29 Palms Marine base. I even found a brass sword hilt in a cave near where LAX is today when I was 11 or so.
My grandmother’s ranch in Chowchilla had quite a collection of Indian mortors that my uncle and my grandfather had turned up when plowing. My cousin still has some of those. They had arrowheads too.