GPS observations in east Siberia combined with global observations, collected 1995--2002, place constraints on the geometry and motions of the Eurasian, North American, and Pacific plates in east Asia. By comparing velocities relative to Eurasia and to North America, we conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate, hypothesized for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity. Smaller plates in east Asia, such as Okhotsk and Amurian, can neither be resolved nor excluded by the GPS velocities.