You mention three sources for obsidian. If one is Glass Mountain - I'm aware of a second in the Coso Range. Where's the third?
Forgotten what it's called, but it's right at the Highway 6 California/Nevada border. Also, I meant to say 3 sites for the southern sierra. Not sure what the northern Native Americans used. One of the sites (can't remember which) has swirls of red in the black obsidian. Another is more clear. You'll also occasionally come across points made from chert -- very red. I think that mostly occurs on the west side. I've even found small sea shells at campsites.
The slope isn't that steep to warrant such an event.
As most all of you have noticed, there are avalanched trees all over the place. Many have obvious slide paths and release all the time during the winter. Others release only on longer-time weather events. One major avalanche year was, I think, '86 when we got about 8 feet of snow in one storm, followed by 10" of rain in a 3 day period. It turned all that snow to a wet slurry and huge avalanches ran within hours of eachother all through the central and southern Sierra. There were 200+ year old Red Firs that were taken down on the East Lake trail (because of the switchbacks, the trail crew would have to cut through the same tree 3 times...). All that water released at once caused major flooding in the Central Valley. Another side note is that many (most?) of California's floods follow that same pattern -- very heavy rain on top of 5+ feet of snow up to 10,000+ feet. It's usually not the rain alone, but the snowpack melting as well.
It's hard to remember, but I think sometime around '93 was another major avalanche year in the central/southern Sierra. Trees down below Center Basin trail are evidence of that year.
But you're right about the one in Tioga meadow. There doesn't appear to be a steep enough slope or accumulation zone to trigger an avalanche. But if you look up from the meadow, there's a very small cirque up there with, if I remember right, a headwall where the west wind will deposit the snow. I've skied that area a few times since and never seen it run again.
The trees were felled by an avalanche about 30 years ago.
Hmmm. Nothing like introducing doubt to my memory. Not impossible but I'm still thinking mid-80s vs. 1980 or so. Still, when I try to dredge up the associated memories to fix it better in time, things get kinda hazy. I definitely remember a bunch of us in Yosemite talking about that slide because we all (ski instructors) thought that area would be a safe place to camp on a winter trip. A good lesson... .