It's quite clear now that Columbia was shedding parts over California, and perhaps earlier. It's starting to look amazing that she made it all the way to Texas. Very interesting article. Check out the time-lapse photo over California, and the animated radar image over Texas.

[Update at 12:30 PM PST]

It just occurs to me that if the Columbia had been headed toward Edwards instead of Florida, the breakup would have occurred far out over the deep waters of the Pacific, and we'd probably have very little physical evidence.

What's the normal track for a landing from ISS at Kennedy? Wouldn't it have been over Mexico, or the Gulf? In any case, it's an interesting coincidence that as a non-ISS flight, it was the first on that path in years. (I remember Oberg would post warnings of such overflights to usenet, especially if at dawn, but not this time.)

I don't know what the "normal" ground trace would be, but I'm pretty sure they can come in from either the north or the south. If the latter, it would come down over Canada, I presume.

If this had been a space station mission, the shuttle would have come and broken up over over Central America, the Yucatan and the Gulf of Mexico, not Texas and Louisiana. And I think America would have reacted very differently indeed. We would never have seen a thing, not astronauts in their last vibrant moments, no doubt trying to solve the problem long after it was hopeless. Instead we'd have been left with the images of a Coast Guard cutter looking for the dead and newscasters pleasing themselves with cheap, predictable ironies about the Columbia 7 dying just miles from the impact which killed the dinosaurs.

The tragic thing is the Shuttle was still transmitting data for several seconds after voice communications with Houston were lost. There's little doubt the astronauts were fully aware they were in a life-threatening situation in the seconds before they died.

Slight nit with that article... the authors did not read the SMU website fully - the 'multiple explosions' recorded by the SMU infrasound group all came from the same direction to within 2 degrees - so the current interpretation is that there was a single explosion, equivalent to 2 to 4 pounds of TNT, somewhere over Lubbock - 50 seconds before loss of contact - and that multiple refracted paths cause the illustion of different arrivals.
The location correlates with the loss of the tire pressure sensors on the left gear - and an unintelligible blurt by the crew.
I believe that was when they knew.