A C180 PILOT REPORTS DEPARTING A SHR ABANDONED RWY THAT WAS SHOWN AS ACTIVE ON HIS BILLINGS SECTIONAL CHART.

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THIS INCIDENT INVOLVES A TAKEOFF FROM A POSSIBLY CLOSED RWY AT AN UNFAMILIAR ARPT; THAT BEING SHR. WHILE TAXIING SW ON THE RWY 5/23 PARALLEL TXWY ENRTE TO RWY 14; WE CAME TO THE FIRST INTERSECTING 'RWY;' SHORTER BUT HEADING DIRECTLY INTO THE WIND. CHKING MY BILLINGS SECTIONAL; DATED 03/07; THE ARPT DIAGRAM INDICATED THREE USABLE RWYS; SO WE COMPLETED OUR ENGINE RUN-UP THERE JUST AS A COMMUTER ACFT BEHIND US REQUESTED WE MOVE TO ALLOW THEM TO TAXI TO RWY 23. WE COMPLIED WITH THEIR REQUEST AND THEN LINED UP FOR TAKEOFF; ANNOUNCING MY INTENTIONS ON THE UNICOM 123.0. BECAUSE OF THE HIGH NOSE ATTITUDE OF MY C180 TAIL DRAGGER; I COULD NOT SEE THE FADED YELLOW X ON THE RWY UNTIL I PASSED OVER IT. AT THAT POINT; THE TAIL WAS COMING UP FOLLOWED BY LIFT-OFF. SINCE THE RWY WAS STILL CLR; IT SEEMED SAFER TO CONTINUE THE TAKE-OFF; WHICH I DID; RATHER THAN ABORT. AN UNEVENTFUL TAKE-OFF WAS MADE FOLLOWED BY A SECOND TRANSMISSION ON THE UNICOM TO ADVISE MY DEP RTE FROM THE TFC PATTERN. WE THEN PROCEEDED TO OUR DEST WITHOUT INCIDENT. CHKING AIRNAV LATER; THE ARPT DIAGRAM SHOWS THE RWY JUST AS THE SECTIONAL CHART DID BUT DOES NOT LIST ANY INFO FOR IT. THE FADED YELLOW X LED ME TO WONDER IF IT WAS CURRENT OR POSSIBLY LEFT OVER FROM PREVIOUS CONSTRUCTION; ETC. IN CONCLUSION I MAY HAVE FAILED TO PROPERLY EVALUATE ALL CONDITIONS AND INDICATIONS EVEN THOUGH THE ENTIRE TAKE-OFF EVENT WAS; IN FACT; A NON-EVENT. IF THE OLD RUNWAY IS UNUSABLE; PERHAPS BETTER MARKINGS AND/OR BARRICADES MIGHT HELP A WAYWARD PLT SUCH AS MYSELF NOT MAKE THE SAME MISTAKE -- IF I DID; THAT IS.