Hello and welcome to RTA !

I am not sure if you are looking for a half way point to SF or to LA ? If you only have 2 days for the complete journey and you need to go to SF then you really need to start out early and get to SF for the night, or at least nearby. The 630 odd miles between Portland and SF will take 11-12 hours with basic stops. Now if you were to stop overnight on route to SF, you could go across to the coast and the Redwoods and overnight in the area and then continue to SF on 101 and over the Golden Gate bridge.