Great pics and history; thank you! A friend that lived in northern California described hiking in the mountains and coming across a small stone marker indicating where a town with thousands of people had been during the gold rush, and now nothing at all remained. He said there were many places like that.
Along the NY/NJ border were settlements like this related to iron mining, furnaces, and forges; as the mines closed there was no need for the woodcutters that fuels the furnaces & forges, the small farms that fed the workers and draft animals, etc. - they all moved on (with small pockets remaining trying sustenance farming). Those areas are all state park land now, but you can still find the settlements by their stone foundations, old roads, and cemeteries.
Chaining the Hudson: The Fight for the River in the American Revolution by Lincoln Diamant.