California has to be one of the best places to visit if for nothing else, but its diversity.  Mountains, the Pacific Ocean beaches, interior valleys, giant Redwoods and Sequoias, great cities and pristine wilderness.  
The Pacific Coast is incredibly beautiful and takes many forms.  San Francisco is a unique city while Los Angeles and its sprawling  perimeter has so many different and varied attractions, I won't even attempt to list them.  If I had to pick only one National Park to visit, it would be Yosemite - in California.  The north shore around San Francisco - Muir Woods and Napa Valley... Pebble Beach and the coast by Monterey and Carmel - the list goes on.  So, I've tried to break up California by various geographic trips we have made.  Choose one - then come back here and choose another.  Enjoy.