That's right, up until a decade or so, Yakima was the repeater for Tri-Cities. Not sure if KLEW in Lewiston had the same set up but I'm guessing when it was still Cascade and then Retlaw, it may have always been a standalone except for programming like Uncle Jimmy. I think KEPR/KIMA represented the first 'satellite' programming in the US, that is, one stations programming being fed by another via telco or microwave. There was also a KBSN TV in Ephrata for a very short time in the late 50's.
Does KAPP even have place to hang their hat on in Yakima? I drove by there out near the airport some years ago and the place was for sale. KNDO hadn't moved yet. I think if it wasn't for the amount of money (KHQ) Cowles Media dumps into 23 and 25, the area wouldn't have much competition, but their Yakima footprint is definitely diminished. KNDU has had a live truck for sometime, a older Ford Explorer which looks like it came from Q6. KEPR's and KVEW' ENG vans look tired.
Getting back to radio, I remember KMSK, they were in downtown Kennewick on Benton St right off 1st ave. It had a tiny office, the studio booth looked out on the street and I got to go inside a couple of times. They changed to KOTY sometime in the 70's and got a FM simulcast too. KALE was also downtown and had the lions share of the market, followed by KONA and KORD, both MOR.