The blackberry bramble to be exact! Today most of my day was spent beating back the blackberry bramble that is only slightly more common here than the poison oak... Indeed when I see something playing the strangler vine on one of the true Oaks here (we have several members of the Querkus family here) or the pines (Sugar, Ponderosa, Digger... etc I don't think Pinion grows here....) I always suspect either one of the two, either poison oak or blackberry bramble.
Now the blackberry here is obviously a member of the rose family, at least that is what the flower looks like, I also suspect that what we really have is a black raspberry but the fruit turns black when it is ripe rather than being red..
Anyway, I've got scrapes and scratches from the briar patch that have probably (reasonably likely) have poison oak oil in them. I saw some poison oak (I was told to avoid it) directly where I was told I had to beat everything as low as possible with the string trimmer...
Anyway, I'm feeling a bit of burn from the poison oak.