Plum pickings: ancient fruit ripe for modern plates

I was pretty thrilled to find my first ripe American plums (Prunus americana) of the season the other day outside Boulder, Colorado. They are quite terrible underripe, but quite delicious once the fruit has some give. I learned a bit about judging ripeness from a friend some years back—look for plums that have just started dropping to the ground. You can pick them up from the ground and from the tree. If gathering from the tree, they should be dropping at the slightest touch. That said, if you g