Yesterday I remotely triggered an R3-D3 SS avalanche on a broad, fan shaped, west facing slope in mid-Mineral Fork, in between the west couloir of Kessler and the East Fork of Mineral. I was about ten turns in when I saw a crack appear underneath my skis; by the next turn, I could see the southern flank of the slab pulling out from a steeper, more northerly terrain feature, about 100 feet to my left and 200 feet downslope. The slide ran into a dense aspen grove, audibly snapping trees up to four inches in diameter. My group of three used the gentle ridge on the N side of this terrain feature to descend, following our skin-track, and we were able to access the debris, making sure there was no evidence other people had been in the runout. We did not approach the crown of this slide. We made a few serious mistakes yesterday. First, we ignored, or failed to take seriously, obvious signs of instability. Along the ridge, we felt a couple relatively small, isolated collapses; we told each other they seemed like they were coming from underneath obvious wind drifts, which themselves were covered in roughly 10 inches of light density, settled, deceptively un-wind-affected snow. Furthermore, we could not see obvious signs of recent avalanches in lower and middle Mineral Fork, although clouds obscured the Room of Doom all morning. At a location where the slope measured 30 degrees and an altimeter read 8300', we walked onto the slope to dig a pit. In 140 cm of snow, we found a Q2 shear, ECTP 15, 75cm from the ground, on very small facets underneath a 1F MF crust. At 60 cm from the ground, we found another Q2, ECTP 23, failing on similarly small facets beneath what I believe was a pencil hard, 2mm thick rain/rime crust from 2/21 or 2/22. There was no dirt layer or late-december rain crust at this location. The snowpit was a couple hundred feet to the north of where this avalanche occurred, and probably 200 vertical feet below the highest portion of the crown, but I am confident the slide ran on one of the shears we found in our snowpit. Our second, more serious error, was in choosing terrain we had only developed an impression of, without really knowing its characteristics. No one in our party had been on this slope before yesterday, although one member of the group and I have remarked on previous occasions that it looked like a great run. Upon reaching the slope yesterday, I thought it looked "low angle," and several slope angle measurements along the flank of the slope adjacent to our up-track were in the low 30's. In yesterday's flat light, it was easy to look all the way across the slope without identifying any terrain features that seemed to be likely spots for an avalanche to release. We projected our slope angle measurements to the open expanse of the slope to our right. After being highlighted by a large crown and mangled bed surface, a broad, very shallow gully in the middle of the face, just to the skiers left of my intended descent route became obvious. I consciously took the appearance of a dense thicket of middle-aged aspens directly at the base of the slope to indicate that this slope rarely, if ever slid. Indeed, it would seem that full-track avalanches on this slope are rare, yet historically occasional events, as just a few, well flagged spruces--with generations of smaller aspen trunks piled up against them--are resident in this stand of forest.

Photos from pba's observation of this avalanche show that I was much closer to the highest portion of the crown than I could tell from above it, or from lower in the drainage, looking back.