There have been two different highways designated as SR 131 at different times since the curent state highway numbering system was first posted in January 1964.
Earlier SR 131
Starting in January 1964, SR 131 began at Jct US 10 US 97 on the NW outskirts of Ellensburg and headed NNW to Jct US 97 at Virden. At this time, US 97 ran coincident with US 10 heading NW from Ellensburg to Teanaway, a few miles east of Cle Elum. At Teanaway, US 97 left US 10 and headed ENE to Virden. I-90 from Cle Elum to Ellensburg opened to traffic in 1967. US 97 was switched to the I-90 freeway route from Ellensburg to Exit 85 then to Teanaway to rejoin the former route. In the 1970s, SR 131 was improved with a wider, straighter roadway. US 97 was switched to the SR 131 route from the Ellensburg area to Virden in 1975. The SR 970 designation was given to former US 97 from I-90 Exit 85 to Virden. The SR 131 designation went into disuse.
Before 1964, SR 131 from the Ellensburg area to Virden had been SSH 2I.
Later SR 131
A different SR 131 was added to the state highway system effective Aptil 1, 1992. The new SR 131 starts at the northern terminus of National Forest Route 25 at the Gifford Pinchot National Forest boundary and heads north to Jct US 12 at Randle. Today SR 131 is 2.07 miles long.
Primary State Hwys Secondary State Hwys