Death Valley is getting warm, but there are historic sites and hikes up side canyons that you spend a week exploring.
I've always liked the Bristlecone Pine area in the White Mountains. It will help a tiny bit with your acclimatization to altitude. More so if you overnight high in the White Mountains. Use sunscreen!
Try to find the SCAA (so cal auto assoc) Owens Valley road map. It has excellent details on attractions, dirt roads, historical ruins, etc. Maybe someone has put it on line?