Elk and Evan's Basins

 Crown investigation of the Saturday afternoon's snowmobile-triggered slab avalanche (South aspect, 12,000', coded here: https://cbavalanchecenter.org/view-observations/#/view/avalanches/8a22e17b-1898-4596-be5d-1065df42c834) suggests that a wet-slab failure mechanism contributed to the instability, even though the slab was mostly dry.  Water had clearly percolated into depth hoar below the February 8th crust.  There were numerous other snowmobile himarks and wet loose avalanches that ran over similar terrain without any slab activity.  

No signs of instability observed under sled.

Crown investigation:  Meltwater from the weekend had percolated through the slab and Feb 8th crust, and had pooled on a grain size boundary between 2mm facets and 2.5-4mm depth hoar.  There were several ice lenses within the slab and weak layer now caused by subsequent refreezing.  See crown profile and photos for details. 

Snow surfaces remained frozen above treeline due to strong winds and some cloud cover, but softened and became wet at lower elevations protected from the wind.  One pit on an ENE aspect (dry snowpack) produced ECTX results but propagated across the column after I gave it a hard stomp with my boot, failing on the Feb 8th facet layer.