Nice! I'm planning a similar route down from Spokane in September. I highly suggest making time to stop and camp at the Alvord Desert. it's a giant playa you can drive out on. and with the Steens Mountains in the background it's gorgeous (also one of the darkest sections of the US so star gazing is epic on a clear night)
I have several POI's you're traveling near and can send them to you.
Fuel is very limited so plan for that, and if wet the mud is SERIOUS, but in Aug it'll more than likely be SUPER dry and Dusty (Highly recommend Amber dust lights mounted High if traveling in a group as the dust can hang forever and make a car disappear 5' in front of you even with brake lights on.)