Complex sentence: For its first eleven years (1986-1997) the show held at Ft. Mason in San Francisco, and for the next eleven years (1998-2008) it was held at the Cow Palace.
Split into simpler sentences: For its first eleven years (1986-1997) the show held at Ft. Mason in San Francisco. For the next eleven years (1998-2008) it was held at the Cow Palace.