C172 PLT CROSSES RWY 26L WHEN GND CTLR AT PUB INSTRUCTS PLT TO 'TAXI TO' RWY 26R.

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THE AIRPLANE WAS PARKED AT THE FBO; FACING NORTH. ATIS RPTED THE WIND FROM 270 DEGS AT 26 KTS. GND CTL CLRED US TO TAXI TO RWY 26R. I TURNED THE AIRPLANE TO THE WEST; TO FACE INTO THE WIND; WHILE I STARTED TO PULL OUT THE TAXI DIAGRAM. ABOUT 20 SECS AFTER THE TAXI INSTRUCTION; GND CTLR INSTRUCTED ME TO TURN RIGHT. I LOOKED TO THE RIGHT (NORTH) AND SAW THE FOXTROT TXWY; READ BACK THE INSTRUCTION; AND TURNED RIGHT; CROSSING RWY 26L AND ENTERING THE FOXTROT TXWY. ATC THEN INSTRUCTED TO BEAR RIGHT AT THE 'Y' INTXN AND HOLD SHORT OF RWY 26R AT THE FOXTROT INTXN. I READ BACK AND FOLLOWED THIS INSTRUCTION. UNTIL THIS POINT; I THOUGHT THAT I HAD CORRECTLY COMPLIED WITH EVERY ATC INSTRUCTION. HOWEVER; THE CTLR THEN ASKED IF I KNEW I HAD CROSSED RWY 26L. I STATED THAT I DID; BECAUSE IT WAS AUTHORIZED WHEN I WAS CLRED TO TAXI TO RWY 26R AND TOLD TO TURN RIGHT. HE REPLIED THAT RWY 26L WAS AN ACTIVE RWY; I DID NOT HAVE PERMISSION TO CROSS IT; AND EMPHASIZED THE DANGERS OF RWY INCURSIONS. I SAID THAT I UNDERSTOOD AND I APOLOGIZED FOR THE MISUNDERSTANDING. IT WAS CLR THAT HE HAD INTENDED I SHOULD HAVE TAXIED A DIFFERENT RTE THAN I DID; BUT I DID NOT UNDERSTAND WHERE THE MISCOMMUNICATION HAD OCCURRED. IF ATC HAD INSTRUCTED ME TO STOP BEFORE CROSSING RWY 26L; THIS INCIDENT COULD HAVE BEEN AVOIDED. THEN HE COULD HAVE CLARIFIED THE TAXI INSTRUCTIONS. I SHOULD HAVE HAD THE TAXI DIAGRAM ALREADY OPEN WHEN TALKING TO GND CTL; BUT I'M NOT SURE I COULD HAVE DETERMINED THE RTE TO TAXI BEFORE I WAS INSTRUCTED TO TURN RIGHT. AFTER THE FLT WAS OVER; I REVIEWED THE TAXI DIAGRAM TO UNDERSTAND THE TAXI RTE ATC HAD INTENDED. I BELIEVE THAT ATC INTENDED ME TO TAXI TO RWY 26R VIA THE RAMP AND TXWY KILO. IF THIS INFO HAD BEEN CONVEYED IN THE INITIAL EXCHANGE; THIS SIT WOULD NOT HAVE OCCURRED. IF ATC HAD NOT BEEN SO QUICK TO GIVE THE INSTRUCTION TO TURN RIGHT; OR IF THE INSTRUCTION HAD CONTAINED MORE INFO (TURN RIGHT AND TAXI W ON THE RAMP...) THEN I THINK WE COULD HAVE CLARIFIED THE TAXI INSTRUCTION. FOR MY PART; I INTEND TO CLARIFY WITH ATC THAT I AM DOING WHAT THEY INTEND; AS WELL AS WHAT THEY SAY. FOR EXAMPLE; INSTEAD OF JUST READING BACK THAT I AM TURNING RIGHT; I WILL ADD 'TO THE NORTH; CROSSING RWY 26L TO FOXTROT TXWY;' SO THAT IT IS UNAMBIGUOUS WHAT I PLAN TO DO. A CONTRIBUTING FACTOR TO THIS INCIDENT IS THAT ATC SEEMS TO HAVE NOT BEEN AWARE THAT THE AIRPLANE WAS NO LONGER FACING NORTH AND THAT IT HAD BEEN TURNED WEST INTO THE WIND. ANOTHER CONTRIBUTING FACTOR IS THAT RWY 26L IS NOT A TYPICAL RWY: IT IS PAINTED ONTO THE RAMP AREA. I DID NOT SEE A HOLD SHORT LINE AND THERE ARE NO SIGNS. I WAS FAMILIAR WITH THE SIT AND I DID THINK I WAS CLRED TO CROSS RWY 26L; SO I CAN'T SAY IF A MORE STD ARRANGEMENT MIGHT HAVE CAUSED ME TO CLARIFY THAT I WAS CLRED TO CROSS THE RWY.