US Highway 10 route changed from the 1937 routing (Seattle - Cle Elum - Blewett Pass - Wenatchee and east to Spokane via today's State Route 2) to the 1944 route (Seattle - Ellensburg - Vantage - Ritzville - Spokane via today's I-90 route).
The cache is not at the posted coordinates, The final is located at N47 06.180 W119 48.ABC . To find the correct coordinates, choose which location did not have US Highway 10 routed by or thru it at any time.
(940) Sprague
(840) Ephrata
(740) Cashmere
(640) Soap Lake
(540) Odessa
Historical Map Source - Washington State Department of Transportation
https://www.flickr.com/photos/wsdot/sets/72157635303976996/