Today was a snowmachine/gear and avy beacon check and refresher day with general recon up SR 20 from Early Winters. Cold temps at Early Winters and warmer temps at higher elevation. Parked at Blue Lake trailhead/SR 20 intersection for lunch and observed the slab release from there. Unable to determine when it happened or trigger. We did not ski or tour off highway. Talked with a solo skier who had skied in area and asked about coverage ( 30" depth at road intersection ). He said generally good but had hit a couple subsurface obstacles on descent. He did not mention slab release during our conversation. Another party of two was skiing in general area and may provide more info. Hoar frost on snow surface with plates in the 0.25" size range where we had lunch.