Of the four IDs I found three belonged to adults; the third was a state ID for a minor related to one of the adults. I was able to find a contact number for all three, via relatives, and had reached them all by afternoon.
I learned that the person who'd dumped the cards had committed a series of car break-ins in San Jose yesterday morning and had fled to Oakland. They stole purses, laptops, and an iPhone. I wish OPD had taken an interest in the theft or at least in returning the stolen property.