Jewish Cemeteries

Hello, non Jew here (friendly Orthodox Christian).

In my home town, an old sparsely populated Gold Mining town that hasn’t been relevant since the gold rush ended has a Jewish Cemetery that’s contained within the Christian Cemetery. The space is separate and contains headstones written in Hebrew and a little bit of English, most of whom died in the late 1800s and early 1900s.

I was curious as to what the significance of the rocks on top of the headstones are?

During the really bad fires of NorCal this summer the Jewish Cemetery was extremely overgrown and there were fires raging in the county. The Jewish part of the cemetery is sort of kept up by a Jewish Organization focused on the preservation of the Pioneer Jews of America but due to Covid they probably didn’t make it out there to keep it maintained. We had some volunteers agree to respectfully clear the weeds because of the fire and noticed that some stones were on top of the headstones. If I would see the stones on the ground in front of the stone I would put it back on the headstone because it seemed intentional.

Did we do anything wrong by doing that? We were respectful and just wanted to make sure the town didn’t burn up, and even though we’re not Jewish it’s still part of the small towns small history.

Anyways, Im curious to know what the stones mean.