Definitely not poison oak, ivy, or sumac, but I'm not sure what it is. I keep thinking it may be some kind of wild grape, but I can't see any tendrils. Did you notice what method of climbing it uses (tendrils, twining, areal roots)?
"...and don't think the garden loses its ecstasy in winter. It's quiet, but the roots are down there riotous." Rumi
