You have to know this region in spain, I have biking in the mountains in the nord or Cáceres: Vera and Jerte Valley.
You have to visit it,

http://www.extremaduravista.com/ingles/rutas.htm
http://www.manbos.com/vergalsitio.asp?galeria=Valle%20del%20Jerte&cod=1

extremadura nice area indeed.
also try grazalema closer to sevilla beautiful park with many trails and friendly folks. I have an English friend residing there he is into natural sites;loves it.