This is a tradition practiced by my informant every Jewish New Year, in Paolos Verdes.
“Instead of going to services, family will go to our local cliff spot and we’ll take a blanket and sit and mom or dad will bring an envelope carrying all of our previous years lettesr and we’ll open them and read all of them to ourselves and become familiar with what our previous years goals were, did we meet them, and we’ll talk to each other about that. And then we’ll get a piece of paper and a pen and we’ll spend some time writing out things that we wish had gone differently, how we would have changed them, and what we wish for the new year. And then we go around and share those if we want, and we seal it. And then we’ll take a couple rocks and think about all the things that we didn’t like about this past year, and following the Jewish tradition where you throw bread, we throw the rocks and “let go” of all the things we felt sad about, or guilty for, or disagreed with in the past year.”
This is a version of the Jewish tradition tashlikh, in which Jews cast bread into the sea to symbolically cast aside their sins from the previous year. It is inscribed in a passage in the book of Micah, 7:18-20, which states “You will cast all their sins into the depths of the sea”. The use of letters and sharing would ensure careful thought and consideration, both personally and among the entire family. The substitution of rocks for bread could be for the ready availability of rocks on a cliff face, but it also might be more healing to throw something heavy as symbolic of sin.