Wild plums. I stopped by the side of a country road to pick a bucket full of these. I think I did it more out of nostalgia. When I was little wild fruits were abundant in the mid-west and those who preserved food had a favorite harvest spot. Sort of like how mushroom hunters operate once they find a location they keep the details to themselves.
These are flavorful but the pit is larger than the pulp area. I'm not a big fan of sugar or I'd cook them down and make a wonderful jam condiment. What I've been doing is giving a few to the chickens each day. The red color and the pit seem to fascinate them. I'll probably find sprouted plum trees in my garden next summer.