I ski cut a small breakover and triggered a 1.5-2' deep slab on surface hoar. 1.5' x 35'. West facing, 9,200', 35 degrees. We were able to trigger some of the hangfire as well. It was quite sensitive and the surface hoar was plainly visible on the bed surface as well as in the profile.
One other skier descended the slope next to the one where I triggered this avalanche and they did not trigger anything, although it was the same aspect, elevation and steepness as the small rollover where I triggered the avalanche. This shows the pockety nature of buried surface hoar.
We saw several natural, shallow, soft slab avalanches at lower elevations along the creek bank in lower Mill D North on steep, east-southeast facing slopes. These were 6 inches of new snow sliding on a pre-existing sun crust. I could not find any surface hoar involved but they certainly acted like it. We saw one slide while skiing up and 3-4 others nearby when we skied down that were not there when we skied up. There was a high precipitation intensity in the morning, which, no doubt, contributed to the shallow instability. Also, the sun poked out at times, which may have added to the stress.