The airplane was being positioned to its home base after it had undergone routine landing gear maintenance and inspection. During the approach to the airport, the pilot noticed that the left main landing gear (MLG) was not down and locked in position for landing. The pilot made multiple attempts to extend the gear and verify a down-and-locked indication without success. After executing the emergency gear extension checklist, the pilot made a low pass at the airport, and personnel on the ground advised over the common traffic advisory frequency that the landing gear appeared to be extended. The pilot prepared for a landing based on this information despite the continued unsafe gear warning annunciation. During the landing, the touchdown was normal, and the airplane slowed normally. After taxiing clear of the runway, the pilot stopped the airplane to complete post-landing checklist items when the left MLG collapsed. The pilot and passenger were not injured. The airplane sustained substantial damage to the left wing. Postaccident examination of the left MLG revealed that the left MLG down lock hook was not properly engaged during the landing.