As I was planting a few fruit trees last weekend, I discovered an odd and very annoying phenomenon. About 6" down from ground level, I ran across a 2" layer of really crumbly concrete/gravel mixture. Beneath that was clay for as far as I dug. The dirt above the concrete layer was slightly better quality topsoil.
I found this in every one of the holes I dug for the trees, which spanned a length over 60' about 10' away from my privacy fence. (The trees were dwarf fruit trees, hence the closer spacing. The recommended separation between trees was 15'.)
At first I thought I discovered some sort of massive French drain covering the entire backyard. But when I looked closer, I realized it wasn't just gravel - it was actually crumbly concrete. Does anyone have any idea why this was in my backyard? And will it significantly affect the trees I just planted?