The private pilot was doing an aerial wolf hunt under Title 14, CFR Part 91. He said he landed the ski equipped airplane on a snow-covered area, but due to the rough terrain, the left main landing gear collapsed during taxi after landing. An inspection of the airplane by an FAA inspector revealed damage to the left main landing gear attachment to the fuselage that required reinforcement of the fuselage, and replacement of the attachment. The pilot said there were no known mechanical problems with the airplane prior to the accident. In a written statement to the NTSB, the pilot said he should have chosen a better operating area.