I think I've found about all the details is on this Wyoming EQ story now.
This is what I know.
My original post was wrong, the mystery quake was 5.3, not 6.5.
It occurred around Newcastle Wyoming on Feb. 6, 2004 at 19:03 GMT.
The event was recorded by at least 3 seismic monitoring agencies, one in the US (USGS), one in France, and the third one from South Dakota, (not a USGS site apparently).
Jim Berkland of www.syzygy.com has also chimed in saying he believes this was a real event.
The event occurred very far from where the elk deaths are occurring, so there is not likely to be any connection there.
Mitch Battros, of EarthchangesTV, is the person pursuing this story with the most zeal.
He contacted several officials at the USGS. He has an e-mail from one of them that states that this event was not an earthquake, but a mine blast. For that reason, the French agency was told to remove the quake from their records. It was also removed from USGS records.
When Mitch presented this explanation to other USGS officials, their response was that because of the magnitude of 5.3, there was no way this could have been a mine blast, unless it was a nuclear mine blast. So that's how the rumor of nuclear testing got started. It originated from conversations with the USGS.
It appears that something DID happen in the Newcastle area that registered 5.3, and the event was ordered expunged from seismic records by the USGS.
Most of this info came from this thread on the TB2000 board.
http://www.timebomb2000.com/vb/showthread.php?s=6045d100fa8be39c54c40936b2c462f0&threadid=93272&highlight=wyoming+earthquake
There was a suggestion on that thread the event was proof from AQ to our gov't that they did have nukes and could detonate them. Could this tie in to daleel's mentioning Yellowstone so much on his earlier threads?
And then there is this
Yellowstone Caldera: Set Up By A "New" and Incredibly Powerful Terrorist Weapon of Mass Destruction
Date: Sun, 8 Feb 2004 00:39:54 -0600
Below is an article on a possible indicator of a most serious strategic potentiality, since it involves a new kind of "weapons of mass destruction" (WMD) strategic threat to the United States (and to the entire Western world) as potent as an all-out nuclear strike from Russia with the Russians firing everything they've got. The actual weapon to be used is an old weapon developed and deployed in the early 1960s, but with a novel application.
From the article, it seems something odd may be going on vis a vis quake reporting also. If this report is true, then the U.S. may have deliberately refrained from reporting a fairly large quake near the super caldera associated with Yellowstone.
If you wish to read the article in its entirety, please click on the link above.