Choosing right site for topsoil to make MTS?
I live in Marina Del Rey CA (part of Los Angeles, just south of Venice). I would like to make MTS. I am trying to figure out how to tell a good place to get the topsoil. I have friends yards or I can go to state parks and grab some soil. I am a little concerned about air pollution debris in the soil too.
The garden center here said we have alkaline soil. There are areas that are sandy but most of the yards I have access to are clay.
I also know someone that has spent years amending their soil from their worm compost. Would that be too high in the npk? Not composted enough? Or would it be a good thing?
Also do I take the top or do I dig down and get it deeper?
Thanks so much,