It's our old friend Toxicodendron diversilobum (aka Rhus diversiloba, or Pacific poison oak, or poison oak, or just "goddamn it"), as viewed on a nice hike last Friday afternoon in Redwood Regional Park in the Oakland Hills. I like the seasonal coloration.
You'd think that the ability to easily spot this plant, and its extra visibility as it takes on fall coloration, might arm you against getting a nice dose of this stuff and the attendant nasty, itching, weeping rash. So you'd think. But you must consider in your calculations the fact you're wearing shorts and the presence of a dog who doesn't know from poison oak and what might happen when you pet the dog and let him rub up against you because you're such an affectionate animal person. Add in the possibility that you neglect to wash your hands or shower off after the hike.
Then you get another kind of fall color, in my case running from my ankles up the inside of my legs all the way to where they aren't legs anymore. I had a bad case of poison oak about 30 years ago, contracted while I was digging on a hillside full of unidentifiable poison oak roots. I have been operating under the comforting illusion that I had somehow inoculated myself against a serious recurrence, and have walked for decades in the hills without much concern about Toxicodendron or its effects (not that I'm careless of it–I watch out for it and try to wash if possible if I think I've come in contact with the plant).
As of this week, illusion gone, for now. The onset of the rash was slow, but by yesterday my lower limbs had blown up to a condition that I call "elephant leg." That's an exaggeration. It's really only "ugly leg." I broke down and called Kaiser, readily got an appointment with my doctor (his schedule had been cleared by patients canceling appointments to go over to the Giants parade in downtown San Francisco), and dragged my unsightly extremities to Oakland. Prescription: a 10-day course of prednisone and what is described as a high-potency steroid ointment. This morning, the ugly is still apparent, but the swelling is going down. I don't lightly resort to such aggressive medical measures, but I'm glad they're there when I want them.