Poison oak, Poison ivy
Poison oak is most common along the West Coast. In the open or in filtered sun, it forms a dense, leafy shrub; in the shade,
it's a tall-growing vine. Its leaves are divided into three leaflets with scalloped, toothed, or lobed edges.
Poison ivy looks similar; it's common east of the Rockies and also grows in eastern Oregon and eastern Washington. Usually found in shady areas and at the edges of woodlands, it sprawls along the ground until it finds something to climb, then becomes a vine.
A resin on both poison oak and poison ivy causes severe contact dermatitis in most people. Control the both with an appropriately labeled herbicide, such as glyphosate (be sure to avoid getting these chemicals on other plants).