Aron Ralston -- the guy who cut off his own arm to free himself from a boulder -- just helped free his girlfriend, too -- from criminal charges.
TMZ broke the story ... Ralston -- the real-life inspiration for the movie, "127 Hours" -- and his GF Vita Shannon were arrested last December in Denver for allegedly assaulting each other during an ugly argument.
Charges against Ralston were quickly dropped -- lack of evidence -- but authorities went after Shannon ... for allegedly punching the one-armed man in the back of the head.
Shannon was in court Wednesday ... and Ralston didn't show up to testify ... so prosecutors dropped the charges.
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