The Ottawa Valley is the valley of the Ottawa River, along the boundary between Eastern Ontario and Western Quebec, Canada. The valley is the transition between the Saint Lawrence Lowlands and the Canadian Shield. Because of the surrounding shield, the valley is narrow at its western end, then becomes increasingly wide (mainly on the Southern Ontario side of the river) as it progresses eastward. The underlying geophysical structure is the Ottawa-Bonnechere Graben. Approximately 1.3 million people reside in the valley (and along its tributaries), of these the majority, around 80%, reside in Ottawa, the remainder on the north side of the Ottawa River, in Quebec. The total area of the Ottawa Valley is 2.4 million hectares (6 million acres). The National Capital Region area has just over 1.4 million inhabitants in both provinces.