Great question! Indeed the east coast (of North America, I presume) sits on a tectonic plate, the same plate that eastern California and New York and everything in between sits on, the North American plate (which extends eastward all the way to the mid-Atlantic ridge).

Practically every place on our planet (under sea or on land) sits on one plate, or micro-plate, or another. The only exceptions are boundaries between plates, such as the San Andreas fault, which divides the North American Plate from the Pacific Plate, and mid-ocean ridges. Some landmasses, such as Iceland, straddle two plates. Indeed North America (geographically speaking) is composed of two plates (geologically speaking). Have fun with Plate Tectonics! Wyss