While skinning up SE-facing aspens (~9000') below Flat Top Mountain, we heard and felt a loud booming collapse. It was unexpected given the spring-like conditions, wet snow, and aspect. We decided to quickly dig down through the shallow (<1 m) snowpack and found an interesting layer of what appeared to look like near-crust facets (?) saturated with liquid water about 30 cms down from the snow surface. We were able to watch the layer collapse with one member of our group jumping on skis above the pit. The layer appeared to be directly below a very visible dust layer within the snowpack (picture).

Further up we saw several old avalanches on SE-facing wind-loaded terrain at ~10,000' (pictures). The dust layer was occasionally visible on the bed surfaces of these avalanches. We saw no signs of old avalanches on any other aspect.

Higher on the ridge at ~10,200' on N-facing slightly wind-loaded terrain we dug an additional pit and found a large (at least 10cm thick) layer of depth hoar at the base of the 1.4 m deep snowpack. We also noted large and deep cracks around a cornice on the ridgetop (picture).