This cache is part of mega cache series on old highways in the Inland Northwest. This cache is on the old route of U.S. 395 (AKA: Three Flags Highway) north of Addy and south of Arden.
When the national highway system was established in 1927, U.S. 395 started in Spokane as a secondary route of U.S. 95, before U.S. 95 was moved into Idaho and U.S. 195 was established to connect U.S. 395 and the other secondary routes of U.S. 95 to said highway. The old route followed the railroad north out of Spokane, going through Chattaroy, Deer Park, and Clayton instead of bipassing the towns. In 1936, the highway was extended all the way to San Diego, going through Ritzville and the Tri-Cities. North of Clayton, U.S. 395 went through Loon Lake and headed towards Springdale (now SR 292 and old Springdale HWY Rd). After going through Springdale, it went north towards Chewelah (on today's SR 231), going through Valley. North of Chewelah, it edged the Colville River valley on present day county roads and driveways.
Washington also had its own highway system. It was called the Primary and Secondary Highway system. Primary highways were numbered routes while secondary routes were letters of the primary route they were conjurent with (I.E: 2, 2G). PSH 3 followed U.S 395 from Spokane to the border. PSH 3 was nicknamed the Inland Empire Highway, starting in Ellensburg, heading down to the Tri-Cities and Walla Walla, and eventually making to Spokane. PSH 3 also was at on time the only place in central Washignton that you could cross the Columbia River via bridge.
The cache is located in the same location as an older cache. Have fun caching :-D