I'm surprised that this isn't included, it's a staple of unexplained incidents lists. I'm really not sure what to think of it due to the lack of evidence, but it's all but official that Israel has nukes, and South Africa wouldn't be that much of a surprise.
Vela Incident - Wikipedia, the free encyclopedia
I did a bit on the Dyatlov Pass Incident in this thread
http://www.tfproject.org/tfp/tilted-...-incident.html and will look to see if I can find a more complete writeup I did of why it's most likely entirely mundane.