PDC here stands for Piedmont Driving Club*. Apparently it was founded in 1887, for driving about the grounds, particularly the racetrack that is now Piedmont Park’s Active Oval (foreground). This year there’s been lots of construction going on there to upgrade the social and athletic facilities, especially along the Park margins, where I could keep tabs on it as I walk—well, on the exterior walls.
Perhaps more pertinent in this photo is the swirling grey sky. Soon after I took this, the drizzle began, which was fine until it became rain—that’s a personal perspective, though, because the plants and water table are probably in better shape because of the precip.
* PDC also stands for, variously, primary domain controller, Portland Development Commission, Professional Developers Conference, Public Disclosure Commission, and Pacific Disaster Center—and that’s just from the first few Google search finds.