The plant shown below puts up new green stalks in early spring, growing to 3 to 7 feet tall. It puts out its yellow flowers in late March or early April (in the Willamette Valley of Oregon), soon after leaves begin to emerge on the stalks. It's in a garden area and not seen elsewhere, so unlikely to be native to the area.
This is Kerria japonica "Pleniflora". K. japonica is native to China and Japan, and has single flowers with five petals, but this variety has been cultivated to have double flowers.
Identifying characterists are the double yellow flowers like pom-poms which are about 1¼ to 1½ inches (3 to 4 cm) wide, the alternate, serrated leaves which start a pale green and darken over the course of the year, and the green bark on newer growth which gradually browns as it ages. It's a multi-stemmed shrub whose stems can grow to about 8 feet tall; they can also trail onto the ground.
Yep. This is a Kerria. Rough thinning will destroy the fragile root system. Cut out dead stems do not pull them out. Mine's nearly dead through harsh treatment. I am in the UK and I dont see a lot if this plant over here either.