Wildlife Spotting

Has shiny leaves, mitten-like structure which made me think it was a form of poison oak, but upon pulling it out I realized it had a tap-root system. This made it seem clearer that it was poison oak of some sort until I saw the nut and shell it came from. Now I'm torn, wondering if it is poison oak or a tree whose nut, in the picture, is seen all across the South Bay of California.