What was found
TUS - ON CLIMBOUT FOR FLIGHT 4172 (TUS-DEN) AIRCRAFT WOULD NOT PRESSURIZE AND RECEIVED A CABIN ALTITUDE MESSAGE. RETURNED TO THE FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. ON POST FLIGHT WALKAROUND FOUND AFT CARGO DOOR WAS NOT FLUSH WITH FUSELAGE. AFT SECTION HAD ABOUT A 1 INCH GAP. SYNOPTIC PAGE SHOWED THE DOOR AS BEING CLOSED. MAINTENANCE INSPECTED DOOR AND AREA AND FOUND NO DEFECTS. DOOR OPERATES CORRECTLY IAW AMM 52-31-00-710-801-A02. AIRCRAFT RETURNED TO SERVICE. NO PARTS REPLACED.