You’re describing the “Scablands”, that totally barren stretch of central WA that was scoured clean by the Columbia river when the Missoula ice dam broke-—Oh, I dunno, a couple bazillion years ago.
The scablands, prairies and sagebrush look pretty nice around the cities, orchards and farmlands because of the great massive irrigation system. Lots of sun, scant rain to ruin the fruit. I got real tired of the gloomy weather on the wet side, especially on the edge of the Cascades where the clouds would pile up and dump some extra moisture. But the weather would clear more often near the Puget Sound. Still, a lot of dense cloud cover. On the East side scattered light cloud cover and it rains in scattered areas not a vast blanket of rain like and heavy laden clouds like “The Dark Side” Especially Forks, the really dark side, lots of lovely moss though.
That reminds me of Mt Shasta in northern CA. It’s very huge and a dormant volcano expected to erupt again. For several miles, huge rocks are scattered around, from the last eruption, whenever that was. I will look.
3,200 to 3,500 years ago