Wind Slab Avalanche on Grouse Rock

We ascended Grouse Rock along the NE shoulder and noticed very large (15, possibly 20 foot) cornices on the east aspect of the ridge N of the Rock. We did not ascend all the way to the ridge, and skied open faces on the SE aspect. Hitting a convex rollover with a small number of buried rocks likely functioning as trigger points, 2 skiers approx 15 feet apart triggered the release of a wind slab of roughly 6 inch thickness. The release propogated, resulting in a crown ~50 feet wide with an inverted V shape. Both skiers escaped but the slide continued 150+ feet down a treed gully.