Reason for flat??? Help!!!!
 

I got a flat tire the other day and took it off of the car. It was the rear left tire, i came to realize that between the tread and the side wall, or the corner of the tire if that makes sense, had been rubbed completely smooth actually to the point where this spot all the way around the tire was concaved back towards the tire!!! i have a feeling that something on the trailing arm is what caused this rubbing to occur and form the nonrepairable hole in the tire. Please let me know if anyone has any idea of what may have caused this. Thank you

Hard to tell by description ... Could be a bad camber toe in alignment issue.

Examine the suspension components for polished areas that might be rubbing
Did you examine the other tire ?