Failed on top of slick crust that I assume formed over the warm weekend. This crust was prevalent throughout our tour at varying depths due to wind during Monday's storm, but generally found about 24" down from the snow surface. Generally this crust was thin very thin and breakable but under the cliff where the slide occurred was about 2" thick. Slide was triggered from snow sluffing off of the rocks above and initially penetrated through the crust directly under the rocks but propagation only occurred above this crust layer.