the time of founding, the swing-span Mission Railway Bridge opened in 1891 was the only crossing of the Fraser River in the Fraser Valley below the Alexandra Bridge, and all rail traffic between Vancouver and the United States was necessarily routed through Mission until the New Westminster Bridge at New Westminster was built in 1904. The rail bridge at Mission doubled duty as a one-way alternating vehicular bridge until 1973, when a long-promised new Mission Bridge was finally completed. The bridge's location is geographically important at the head of the tidal bore on the Fraser River, and its water level gauge is an important measure of the Fraser's annual and sometimes dangerously large spring freshet. Mission City's original retail core was in the small area of lowland between the CPR mainline and the river. Following the great flood of 1894 a few years after the town's founding, the core was relocated just north of the rail line at the foot of the hillside rising above the rail junction. This small commercial strip, originally named Washington Avenue, later Main Street and since the 1980s called First Avenue, is only four or five blocks long and was one of the principal commercial centres of the Fraser Valley for many decades and had a lively retail trade and social life. Following the 1894 flood, abandoned buildings and lots in the old downtown were taken over by Chinese merchants and workers, creating a Chinatown which lasted until the 1920s. The western part of the district, the Stave Valley, is largely rural and forested but its watercourse is home to what was the largest hydroelectric project in British Columbia until the Bridge River Power Project opened in 1961. It was built by the British Columbia Electric Railway (BCER) to provide power to the electric street railway and interurban system in Vancouver. The Stave Falls Power Co. operated a light-gauge railway for passenger and freight service up the lower canyon of the river to the dam at Stave Falls. During the construction of the Ruskin Dam (completed 1931) the railway was rebuilt at a higher elevation so as to skirt the new Hayward Lake reservoir. The rail line has long been discontinued, but the old grade and its trestles are now part of a recreation trail circling the reservoir. Flanking the outraces of the powerhouse at Stave Falls there was once a fairly large community (300