Same thing (disappearance of dry stone walls) happened in my native Kentucky during my lifetime. I well remember, as a child, back in the 1960s, gazing at the beautiful, bucolic landscape.....rolling green pastures delimited by limestone fences. Now, most of those fences are either gone, or have fallen into shameful disrepair.
One of the things I miss about New England are all the stone walls snaking off into the woods. Most are also in disrepair, but one of the ideas about their construction was as a sort of stone holding area--a way for the farmers to store the stones that came each plowing season, as well as to define fields. Not much need for that anymore since small scale farming is pretty much gone from that area.
Anyone who has dug around in New England knows unless you are in a floodplain, you are going to be hittin rocks. When I was working as a contract archaeologist there, we used to go through so many shovels each digging season. Dig dig *clang* "Ouch". :)