Subject was dug out when I arrived and was being treated by Life Fight nurse. Father and son were sledding on the Ant Knolls face and they both jumped the cornice and rode down the 40+ degree east face. On the 3rd junp, the father triggered the slide and tried to ride it out but was caught carried about 800' down and was pinned up against a 3" trunk diameter pine tree at toe of the slide and was partially burial with serious injury to leg and ribs. His son was carried down but only partial buried and was not injured and was able to rend aid to father quickly. We carried the father about 150 yards down to Life Flight. The Son rode his snowmobile out.