On August 16, 2000, about 1700 Alaska daylight time, a tundra tire equipped Cessna 185 airplane, N185M, sustained substantial damage during landing at an off airport landing site on the Alsek River, Alaska, at 59 degrees, 04 minutes north latitude, 138 degrees, 19 minutes west longitude. The commercial pilot and the two passengers were not injured. The flight was conducted under 14 CFR Part 135, by Mountain Flying Service, Inc., of Haines, Alaska, as an on demand sightseeing flight. The flight originated from Haines, Alaska, about 1500, with a planned landing at the accident site. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The pilot told the NTSB investigator-in-charge during a telephone interview on August 21, that during the landing on firm sand, the right landing gear leg separated at the wheel attachment upper bolts. The remaining gear leg dug into the sand, and the airplane spun around. The airplane sustained substantial damage to both main landing gear attachments, and both wings. The fractured lower leg was examined at the NTSB materials laboratory on September 12, 2000. Areas of fatigue were found at both upper bolt holes. Corrosion pitting was found at one of the fatigue sites. Pink, non-destructive inspection, dye penetrant residue was found inside the bolt holes. A review of the airplane's logbooks revealed that the airplane had been operated on skis in the past.