On February 8, 2000, about 1300 Alaska standard time, a ski-equipped Cessna 180 airplane, N4961A, sustained substantial damage while landing at Caribou Lake, about 30 miles west-southwest of Glennallen, Alaska. The solo commercial pilot was not injured. The 14 CFR Part 91 personal flight departed Nabesna, Alaska, about 1130, and was en route to Anchorage, Alaska. The flight operated in visual meteorological conditions without a formal flight plan. During a telephone conversation with the NTSB investigator-in-charge (IIC) about 45 minutes after the accident, the pilot related he made an intermediate stop at Caribou Lake to wait out deteriorating weather conditions. During the landing roll, the left main landing gear ski encountered deep, drifted snow, and the airplane turned to the left, nosed over, and received substantial damage to the left wing, vertical stabilizer, and rudder. The pilot reported there were no preaccident mechanical problems with the airplane, and that he just didn't see the drifted snow in time to avoid it.