ALT:BEER:RECIPE from Brewing Classic Styles. It is a great beer brewed with lager yeast to, if you can't get the alt yeast. I would not replace Magnum. I am using Carafa S1 instead of Carafa S2, because that is what I have at hand. Same amount though, mostly a color issue. I also scale down a bit on the griest when using Lager yeast due to attenuation.
First try at a California common using ingredients on hand.