More common in the West, especially California, is the related Poison Oak, Toxicodendron diversilobum. The lobes of its leaves are more rounded at the tips. In strong sunlight the leaves tend to be smaller and a darker green, while in shady areas they can be quite large and paler. Poison Oak can grow as a shrub OR vine.
Seldom mentioned is the fact that after the leaves come off in the Fall, the bare stems are equally dangerous, perhaps more so as they are harder to recognize. The main stems tend to extend outward from the base of the plant in upward-curved fashion, with short (4-8 inches) side branches. The overall appearance is of long, curved fingers like a cupped hand. Certain identification is easy if you also notice a few lingering white berries, or if you see a broken stem revealing BLACK dried sap around its edges (something to watch out for when seeking a good marshmallow-roasting stick!)
Good point! I never knew poison ivy bloomed or produced berries until I started researching this article, so I wanted to be sure to include pictures of the berries and the leaves in different seasons. Identification without either of those features would be really difficult! The very thought of using it as a marshmallow roasting stick gives me the shudders.