Fraser Lowland in the context of "Catchment"

The Fraser Valley is a geographical region in southwestern British Columbia, Canada and northwestern Washington State. It starts just west of Hope in a narrow valley encompassing the Fraser River and ends at the Pacific Ocean stretching from the North Shore Mountains, opposite the city of Vancouver BC, to just south of Bellingham, Washington.

In casual usage it typically describes the Fraser River basin downstream of the Fraser Canyon. The term is sometimes used outside British Columbia to refer to the entire Fraser River sections including the Fraser Canyon and up from there to its headwaters, but in general British Columbian usage the term refers to the stretch of Lower Mainland west of the Coquihalla River mouth at the inland town of Hope, and includes all of the Canadian portion of the Fraser Lowland as well as the valleys and upland areas flanking it. It is divided into the Upper Fraser Valley and Lower Fraser Valley by the Vedder River mouth at the eastern foothills of Sumas Mountain, although the Lower Valley section upstream of McMillan Island and the Salmon River mouth (at Fort Langley) used to be called the Central Fraser Valley up until 1995 (see Central Fraser Valley Regional District).

Sumas Mountain, also referred to as Canadian Sumas to distinguish it from an identically named mountain just 10 km (6.2 mi) to the south in U.S. state of Washington across the border, is a mountain in eastern Fraser Lowland, in the Lower Mainland region of the Canadian province of British Columbia. It sits on the south bank of the Fraser River, west of the smaller Chilliwack Mountain across the Vedder River mouth, and serves as a geographic landmark dividing the Fraser Valley into "Upper" and "Lower" sections. Sumas Peak is an official name for the summit located on the south shore of the Fraser River in the Fraser Valley between Abbotsford and Chilliwack. Elevation 910 m (2,986 ft) above sea level, prominence 875 m (2,871 ft).

The mountain is separated from the Vedder Mountain and the North Cascades by the drained Sumas Lake, now a flatland referred to as Sumas Prairie that is part of the greater floodplain of the Fraser River basin, south of which is a same-named sister mountain—American Sumas—in Washington's Whatcom County. 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.