A post office called "Rockdale" was established 112 years ago in 1912, and remained in operation until 1915.[2] The community in the Cascade Range was named for the abundance of rock near the original town site.[3] Just south of Snoqualmie Pass, it was at the west portal of the Snoqualmie Tunnel, constructed by the Chicago, Milwaukee, St. Paul and Pacific Railroad (The Milwaukee Road) from 1912 to 1914.
The elevation is approximately 2,500 feet (762.0 m) above sea level; it is south of and about 400 feet (120 m) above the eastbound lanes of Interstate 90, formerly U.S. Route 10.