Hyak was established around 1915 at the eastern portal of the Snoqualmie Pass Milwaukee Road Railroad tunnel. 
Old box at the end of the Snoqualmie TunnelSnoqualmie Tunnel (Wikipedia) The Snoqualmie Tunnel is a former railroad tunnel near Snoqualmie Pass in the U.S. state of Washington, located east of Seattle. The tunnel crosses the Cascade Range about three miles (5 km) south of the pass, which is used by Interstate 90, on the border between King County and Kittitas County. It is 11,894 feet (2.253 mi; 3.625 km) long and is at an approximate elevation of 2,600 feet (790 m) above sea level, just north of Keechelus Lake. Its east portal is at Hyak. 
Under the Snoqualmie Tunnel