As we walked the upper days ridge from two dogs to true flagstaff, I noticed a big crack appear underfoot. Looked back towards two dogs and saw the entire slope folding on itself about 50' down and sliding. It propagated big, ripping out the shot skiers left two dogs and extending far into the North facing terrain. Intially we thought it propagated all the way to Jaws, but as we got in the basin later we noticed it only went to the skiers left shot of oingo boingo, propagating approx 600' wide. Crown was varying in size and we couldn't get close to it safely, but it was appeared to be 3-4' in spots. It slid to bed surface and ripped thru the flats where everyone transitions below. Still plenty of hangfire sitting atop two dogs that didn't release.