CL65 FLC LINE UP WITH THE WRONG PARALLEL RWY AND SUBSEQUENTLY THE FO NOTICES THE ERROR AND CALLS FOR A GAR.

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WE WERE ON A STAND-UP (CONTINUOUS DUTY) TRIP WITH APPROX 4 1/2 HRS OF SLEEP. ON INITIAL CONTACT WITH APCH; WE WERE TOLD TO EXPECT RWY 18R. COMING FROM THE SE; USUALLY RWY 18L IS ASSIGNED; BUT OCCASIONALLY ATC WILL ASSIGN RWY 18R (USUALLY STATING THAT IT WILL BE A L OR R DOWNWIND). ATC DID NOT STATE WHAT DOWNWIND TO EXPECT. WE WERE SWITCHED TO ANOTHER CTLR AND TOLD TO DSND TO 7000 FT. I DO NOT REMEMBER IF SHE REAFFIRMED RWY 18R AS THE ASSIGNED RWY. BEING A VFR DAY AND LITTLE TFC; WE WERE TOLD TO DSND AND GIVEN A TURN TO BASE AND CLRED FOR THE VISUAL APCH. WE HUSTLED DOWN AND TURNED FINAL INSIDE THE OM. WE WERE CLRED TO LAND AND PERFORMED THE LNDG CHKS. I NOTICED THAT WE WERE ON GS BUT WE LOOKED LOW AND SHORT. I BECAME PREOCCUPIED WITH THIS CONFLICTING INFO AND FAILED TO NOTICE THAT THE LOC WAS DEFLECTED FULL R. THE FO STATED THIS WAS NOT RWY 18R; AT WHICH TIME I CALLED FOR A GAR. WE PERFORMED A GAR AND NOTIFIED TWR. TWR ASKED WHAT THE REASON FOR THE GAR WAS AND WE STATED WE WERE LINED UP WITH THE WRONG RWY. CONTRIBUTING FACTORS: PHYSICALLY AND MENTALLY TIRED (THE MAIN REASON). LACK OF CTLR CONFIRMING RWY (THOUGH I HAD BRIEFED THE CURRENT RWY).