A CESSNA 310Q OVERRAN RWY 30 AND COLLIDED WITH TERRAIN OFF THE DEPARTURE END. A WITNESS STATED THE ACFT LANDED AT APRX MID-FIELD ON THE 2,485 FT BY 50 FT ASPHALT RWY AND WAS UNABLE TO STOP. BASED ON THE WITNESSES' STATEMENT APRX 1,240 FT WOULD BE AVAILABLE FOR LANDING. THE PLT REPORTED TO THE FAA THE WINDS WERE CALM AT THE TIME. THE AIRPORT MASTER RECORD INDICATES THAT THERE ARE 50 FT TREES LOCATED 400 FT ON A 130 DEGREE RADIAL FROM THE DISPLACED THRESHOLD. RWY 30 HAS A 380 FT DISPLACED THRESHOLD LEAVING 2,105 FT REMAINING FOR LANDING TOUCHDOWN AND ROLLOUT. THE OPERATORS MANUAL FOR THE CESSNA 310Q INDICATES AN APPROXIMATE DISTANCE OF 1,500 FT WOULD BE REQUIRED TO LAND OVER A 50 FT OBSTACLE. ACCORDING TO THE POLICE REPORT, THE PLT INDICATED THAT HE HAD MADE A NORMAL APPROACH AND LANDING, BUT THE ROLLOUT WAS 'LONGER THAN NORMAL.' THE PLT DID NOT INDICATE TO THE POLICE THAT THERE WAS ANY MECHANICAL FAILURES OR MALFUNCTIONS.