For railroad buffs, the Railroad Museum in Sacramento is a must.

heric's remarks about heat on 395 and into Yosemite being mighty hot and less interesting in the summer also apply to the route I suggested- 95 to Tonopah, and across to Yosemite.

It's hard to suggest a route from Las Vegas. Cutting west from Nevada, we took the Virginia City (interesting) Reno route, since an early stop in CA had to be Sacramento, where we have relatives.

Why Las Vegas ? Unless you have friends, relatives or like the shows they do there.