After listening to all the observations of various people in California it is apparent to me that the Shuttle problem started when something popped off the orbiter as it flew north of San Francisco, or maybe even a bit earlier. The first anomalies began at 8:53, exactly the time when the Shuttle was to fly directly north of San Francisco. People have reported seeing things break loose at this time and shortly after.

The only ground track I can find is the crappy one on the NASA Shuttle page, since all the ground tracking applications I am aware of have taken the Shuttle's data offline.

If something came off, the following problems would indicate that this something was a piece of thermal protection. If so, it's somewhere in eastern California or Nevada, since it wouldn't have burned up.

This is of course assuming the tile was even there before reentry, in which case what people saw breaking off were probably small chunks of whatever the tile was protecting, and there may be no surviving debris from this.