We skinned the ridge between West Porter and Thaynes. We transitioned at 9000' to head down. As we were transitioning we heard a rumble that quickly turned to quite a roar. We looked to our west and saw a powder cloud charging down the next drainage over, along with the sound of large trees snapping. We were not able to get a view of the slide. Seemed to initiate off the top of what is commonly called "West Porter peak", down a steep N/NW facing line, running far into the lower angled terrain below. Wish we were able to get a better view, as this slide sounded very destructive.