New snow avalanche Northern Bridgers

After skiing two laps on East facing terrain two basins north of Anger Lake basin and seeing no significant signs of instability, we descended into a north facing gully around 8,200ft and triggered an avalanche on the new snow/old crust interface. The crown was 4-18 inches deep and propagated the entire width of the gully ~40 feet and ran the entire length of the gully ~500 vertical feet. I was able to ski out of the avalanche right as it broke and was not carried.