Virginia has five main geological regions, each differentiated by rock strata and elevation. First is the Tidewater area on the coast of Virginia and the southern Chesapeake Bay, both of which lie within the same coastal geological plane. Second is the Piedmont bioregion, defined geologically by igneous and metamorphic rock and cartographically with a diagonal swath bordered on the east by the Tidewater area and on the west by the rising Blue Ridge Mountains. Third is the Blue Ridge and, fourth, the Shenandoah Valley—an area sometimes referred to as the breadbasket of the state. The fifth zone, the Appalachian Highlands, includes mountains to the west, parts of which are sometimes referred to as the Highlands.