A BELL HELICOPTER 206L-3 COLLIDED WITH WIRES WHILE MANEUVERING OVER AN UNDERGROUND TELEPHONE CABLE. THE PLT INDICATED THAT HE HAD JUST COMPLETED A 360 DEG RIGHT TURN AT THE REQUEST OF THE PAX AND WAS APRX 185 DEG THROUGH THE SECOND TURN WHEN HE STRUCK A UNMARKED SINGLE STRAND POWER CABLE. THE PLT NOTICED A BRIGHT ELECTRICAL FLASH IN THE AREA OF THE ACFTS WINDSHIELD CENTER POST. HE IMMEDIATELY ENTERED AUTOROTATION AT APRX 80 FT AGL AND 60 KTS INDICATED AIRSPEED. THE TERRAIN BELOW THE ACFT WAS A VEGETATED DRY FLAT SANDY WASH. THE HELO LANDING HARD COLLAPSING THE SKID TYPE LANDING GEAR AND THEN ROLLED OVER ON ITS RIGHT SIDE. THE PLT ALSO STATED THAT HE DID NOT SEE THE WIRES PRIOR TO THE COLLISION. THE WIRES WERE STRUNG ACROSS THE WASH WITH THE POLES MASKED BY CANYON WALLS ON EACH SIDE OF THE WASH. THE PLT DID NOT GIVE ANY INDICATION OF MECHANICAL FAILURE OR MALFUNCTION.