Sumas Mountain, also referred to as Canadian Sumas to distinguish it from an identically-named mountain just south in Washington state, is a mountain rising from the floodplain of the Fraser River in the Lower Mainland of southwestern British Columbia, Canada. Its western end is in the urban area of Abbotsford and is home to a number of suburban areas of that city, notably Clayburn. In its central portion is the historic community of Straiton, officially named in 1904 for Thomas Bell Straiton who founded a homestead on Sumas Mountain in 1893 and also a store and post office. Its higher eastern reaches tower over Greendale, a community within the City of Chilliwack and is mostly wilderness; the mountain's summit, Sumas Peak, is located in this area, along with Chadsey Lake. The mountain is separated from the Cascade Mountains by the drained lake now called Sumas Prairie, south of which is its American sister, Sumas Mountain, and which is part of the greater floodplain of the Fraser River (the Fraser Lowland). West of the mountain is Matsqui Prairie, another floodplain, and north of the Fraser, which lies along the mountain's north flank, are similar floodplains - Nicomen Island and Hatzic Prairie.