The Ottawa Valley is the valley of the Ottawa River, along the boundary between Eastern Ontario and the Outaouais, 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 and then becomes increasingly wide (mainly on the 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), around 80% of whom reside in Ottawa. The total area of the Ottawa Valley is 2.4 million ha (6 million ac). The National Capital Region area has just over 1.4 million inhabitants in both provinces.