First, thanks everyone for the immediate answers. It is very nice to see, that aviation forums all over the world are a nice place to hang out. Our Swiss forum flightforum.ch (only in German) is very helpful as well.
But coming back to all the suggestions:
I did my Cirrus SR-20 training in Loveland, Ft. Collins (KFNL) last October and logged around 16h with this plane now. So I will see if the guys from Justice Aviation in KSMO will lend it to me.
Big Bear sounds nice, but as everybody said, DA might be a problem. I'm travelling with a business partner, so we will be not bad on the weight. Still, I went to Aspen from Ft. Collins last year and even with the colder weather we had a very high DA and the SR-20 is not a rocket anymore there.
Mojave and Victorville sounds tempting, but the rest of the journey sounds rather boring. I did the trip last night in my Flight Sim. Not much to see once you are outside the L.A. area.
Would you rather suggest to fly to Las Vegas commercially and the rent a plane there. What would be the places to go from there. Grand Canyon of course and the Page? Would you have any tips for a 2-3 day tour from and back to L.V.? Where to rent in Las Vegas. I wrote an e-mail to a coule of FBO's and did not get any answers.
@Silvaire1: I enjoyed the area around Colorado already, your mountains are a lot higher than ours. Where did you fly in Switzerland?
Regards,
Marcel