http://www.facebook.com/pages/Patagonia-MTB-Tours/109162849120258 Thats the site of a friend who would guide you at San Martin de los Andes showing you great trails. Also, He is a top guy!

"Riding around San Martin de Los Andes is fast and furious. And dusty. Don't be the rider at the back" Certainly I -and my scars- can tell! Hehe. Also in summer at San Martín de los Andes and San Carlos de Bariloche there are bike parks at Chapelco and Cerro Catedral Sky Resorts. In three weeks I'll be riding there :)