Pelirrojos (check your dictionary...) are definitely in more abundant "supply in Galicia and Asturias. Of course, they're outnumbered by pelirrubios, but as correctly commented prior, the Celtic influence in this area is strongest, and still remains so.
Spain and the U.S. seem to have that in common: The further south you travel, the more "moreno" people tend to be (with exceptions of course). The rubios only like to vacation to the south (see Arizona, California and the Costa del Sol :cool
. I grew up in Minnesota and wondered why the Swedes and Danes would settle there...until I went to Sweden and Denmark...spitting image as far as countryside.
I'm certain that's why the Celts stayed so long in Spain, and why their influence still remains: They settled a region not unlike their own.