Those look like Montmorency cherries to me. Maybe they're just under-ripe Bings though. Suuuuper impressed by the Forage Oakland (and apparently Forage SF) effort. Sent this to them yesterday:
I have a large Meyer lemon tree in the Mission/ SF. Not really any lemons now, but there sure will be. Herbs in the backyard pots, happy to share small quantities with nearby neighbors.
Interested in stone fruit (especially plums and apricots) and unusual citrus varieties. Always willing to trade fruit for preserves.
Very happy to help you with the project. A google map of this stuff would be awesome. I'm a bit of a geek (my job is to help large nonprofits with internet strategy) and admittedly a food nerd...
Will report on the much-anticipated outcome.