The crew of a firefighting Lockheed SP-2H Neptune (Air Tanker mod.) N355MA, “Tanker 55”, reported it was unable to lower its left main landing gear and force landed at Minden-Tahoe Airport, in western Nevada. That crew had been helping with efforts to fight the George Fire within the Giant Sequoia National Monument in California. When on approach to Porterville, California, the main landing gear showed unsafe on port side. The pilot aborted the landing and climbed above pattern altitude where the landing gear was cycled again with same results. The left gear would not extend. A decision was made to return to the company’s base at Minden-Tahoe Airport where contact was made with operations and maintenance personnel. After all emergency procedures and maintenance ideas were exhausted the pilot executed an emergency landing on runway 16 with main the left gear still in the up position. The nose and starboard gear were down and locked. After touchdown and bleeding off airspeed, the aircraft settled on the port jet pod and sustained left engine propeller strikes. As the aircraft came to a stop, the left jet pod pylon broke off, while being sideloaded from a side motion skid. There is no apparent damage to the wing structure or pylon attach points. Pilot and co-pilot exited the aircraft with no injuries.