The Fraser River is the longest river in British Columbia, Canada, rising near Mount Edith Cavell in the Rocky Mountains near Mount Robson and flowing for 1400 km (870 mi), into the Pacific Ocean at the city of Vancouver. Much of B.C.'s history has been bound to the Fraser, partly because it was the essential route between the Interior and the Lower Coast after the loss of the lands south of the 49th Parallel with the Oregon Treaty of 1846. It was the site of its first recorded settlements of Aboriginal people (see Stó:lo-, St'at'imc and Nlaka'pamux), the route of multitudes of prospectors during the gold rush and the main vehicle of the province's early commerce and industry. The Fraser drains a 220,000 km² area. Its source is just below Mount Edith Cavell, and for the first part of its course it runs northwest, past Mount Robson, reaching past 54° north before making a sharp turn to the south. At the city of Prince George it is joined by the Nechako River, then continues south and slightly east until just north of the United States border, where it issues from the Coast Mountains from a deep canyon a few hundred miles long. It then turns west through a lush lowland valley, known as the Fraser Valley, past Chilliwack, Abbotsford, Mission and the eastern suburbs of Vancouver. After 100 kilometres, it forms a delta where it empties into the Strait of Georgia between the mainland and Vancouver Island. The lands south of the City of Vancouver, including the cities of Richmond and Delta sit on the flat flood plain. The river's volume at its mouth is 112 km³ each year, and it dumps 20 million tons of sediment into the ocean. The upper reaches of the Fraser River were first explored by Sir Alexander Mackenzie in 1793, and fully traced by Simon Fraser in 1807, who confirmed that it was not connected with the Columbia River. The Fraser is heavily exploited by human activities, especially in its lower reaches. Its banks are rich farmland, its water is used by pulp mills, and a few dams on some tributaries provide hydroelectric power. The main flow of the Fraser has never been dammed so as not to interfere with salmon spawning. Today, Fraser Herald at the Canadian Heraldic Authority is named after the river. The delta of the river, especially in the Boundary Bay area, is an important stopover location for migrating shorebirds.