SMA MULTIPLE RWY OP INTERSECTING RWYS HAD RWY INCURSION CAUSED ACFT GAR.

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DID ILS APCH TO RWY 16. ASKED TO KEEP AIRSPD UP. KING AIR FOLLOWING. ASKED TO HOLD SHORT OF RWY 24. ACKNOWLEDGED. ATC WAS VERY BUSY. IT WAS OBVIOUS THAT OPS ON RWY 24 WERE BUSY. AFTER LNDG TOLD TO TURN L AND HOLD SHORT OF RWY 24. ACKNOWLEDGED. DON'T REMEMBER EXACT CTLR TERMINOLOGY. TURNED L OFF RWY 16. THOUGHT I WAS ON A TXWY NOT DEPICTED ON CHART. DID NOT THINK MY LNDG HAD TAKEN ME AS FAR AS THE INTERSECTING RWY. HAD CURRENT ARPT DIAGRAM IN FRONT OF ME. SAW RED RWY 6/24 SIGN. CONTINUED; WAS LOOKING FOR YELLOW HOLD MARKINGS ON TXWY. DID NOT REALIZE I WAS ON RWY 12L/30R. SAW SOME ASPHALT OFF TO L. THOUGHT IT WAS SOME TYPE OF ACCESS ROAD NOT ON CHART. REALIZED I WAS ABOUT TO CROSS A RWY 24 SO STOPPED IMMEDIATELY. NOSE OF ACFT WAS VERY CLOSE TO EDGE OF RWY. MAYBE A LITTLE OVER. DON'T REMEMBER EXACTLY. I CERTAINLY WASN'T IN THE MIDDLE OF THE RWY. SAW CESSNA ON SHORT FINAL. ABOUT TO CALL CTLR WHEN THE CTLR CAME ON FREQ AND TOLD CESSNA TO GAR; AIRPLANE WAS ON THE RWY. IF CESSNA HAD LANDED; WE WOULD HAVE BEEN UNCOMFORTABLY CLOSE. GAR WAS THE RIGHT ACTION. TOLD TO CROSS RWY 24 AND CONTACT GND. I APOLOGIZED AND INDICATED I HAD BEEN LOOKING FOR A HOLD SHORT LINE. CTLR INDICATED I HAD STOPPED IN THE MIDDLE OF THE RWY. I DID NOT SAY ANYTHING BUT THAT WAS NOT EXACTLY THE SIT; BUT I WAS TOO CLOSE TO THE RWY. IF I HAD BEEN ON THE RWY; I WOULD HAVE CONTINUED ACROSS WHEN I SAW THE AIRPLANE. I THOUGHT THERE WAS ROOM FOR THE PLANE TO LAND EVEN THOUGH IT WOULD HAVE BEEN UNCOMFORTABLY CLOSE. I WAS GLAD THE CTLR TOLD THE PLANE TO GAR. AFTER SOMEWHAT TENSE LNDG WITH XWIND; KING AIR FOLLOWING; BUSY FREQ; I LOST POSITIONAL AWARENESS ON AIRFIELD. DID NOT TRUST CHART WHICH IN RETROSPECT IS VERY ACCURATE. EVEN THOUGH RWY 6/24 IS REFLECTED ON CHART AS SLIGHTLY NARROWER; I WAS LOOKING FOR A MORE OBVIOUS RWY. AFD NOTES INDICATE RWY 6/24 LOOSE SURFACE; CRACKS AND DIPS IN PAVEMENT. I DO NOT RECALL THESE REMARKS EVEN THOUGH I HAD READ BOTH AFD AND AOPA DIRECTORY. DON'T REMEMBER IF CTLR TOLD ME TO TURN L ON RWY 12L AND HOLD SHORT OF RWY 24 OR JUST TURN L AND HOLD SHORT OF RWY 24. I THINK THE INSTRUCTION WAS TO TURN L AT NEXT INTXN CAUSING ME TO THINK I WAS ON AN UNCHARTED TXWY AND LOOKING FOR HOLD LINE ON PAVEMENT. I'M SURE THE SIGNS AT THE INTXN OF RWYS 16 AND 12L INDICATED I WAS TURNING ONTO A RWY; BUT I DON'T RECALL. I JUST HAD A STRONG IMPRESSION I WAS ON A TXWY. MAYBE THE CTLR SHOULD GIVE INSTRUCTIONS LIKE TURN L ON RWY 12L AND HOLD AT RED RWY 6/24 SIGN. THAT WOULD OF HELPED MY SIT.