How did this happen? There was obviously more wear on it then the others but I am not understanding it. Do I have an issue here and if so how do I go about fixing it? Thank you very much!

How did this happen? There was obviously more wear on it then the others but I am not understanding it. Do I have an issue here and if so how do I go about fixing it? Thank you very much!
A caliper problem I'd guess...either the side that is worn/grooved is not releasing fully, or the other side is not working.

Like mongo said, probable cause is a worn caliber pin. Possibly a bad caliber, but I would bet on the pin.

:iagree: unless you are a do it your self kind of guy i would have that looked at a lot of shops will do a free brake inspection but dont let it go it will cost you a lot more in the end if you do