and the year of their establishments. SR 123 is in the center and was established in 1923 as a branch of . The history of SR 123 begins with the establishment of the
Pacific Forest Reserve in 1893, which became the
Mount Rainier Forest Reserve on in 1897, both included the area near the present highway. The
Mount Rainier National Park was established as the fifth
national park on March 2, 1907. The Mount Rainier National Forest Reserve became the
Rainier National Forest in 1907 and
Columbia National Forest in 1908. The northern terminus of the roadway at Cayuse Pass became (US 410) during the creation of the
United States Numbered Highways. The Columbia National Forest replaced the Rainier National Forest in 1933. Between 1946 and 1959, a
ski resort operated at Cayuse Pass. In 1949, the Columbia National Forest was renamed to the
Gifford Pinchot National Forest to honor a
pioneer of the same name. During the
1964 highway renumbering, the Cayuse Pass branch of PSH 5 became , an
auxiliary route of . SR 14 became on June 20, 1967, and SR 143 became SR 123, while US 410 became . Since 1974, the
Washington State Department of Transportation (WSDOT) has recorded the opening and closing dates of Cayuse Pass. The only season when the pass was not closed was between 1976 and 1977. The earliest closure was on October 7, 1996, and the earliest opening was on March 30, 1992. The latest closure was on January 4, 1990, and the latest opening was June 21, 1996. After the
Hanukkah Eve windstorm of 2006, a long segment of SR 123, which is only long, ==Major intersections==