This is a link to a USDA publication about Prunus Americana Marsh which are the wild sandhill plums that we gather here in the great plains. Copy and paste into your browser. They do make lovely jelly and wonderful wine!
I can't remember the amount of times my mother and I would be going somewhere and along a fenceline she would see a sand plum thicket. we would pile out and get to pickin'. I live in Ok and they are all over in the sandy areas of northwest OK.