On September 10, 2006, at approximately 1830 mountain daylight time, a Maule M-4-180V, N786ST, was substantially damaged during a landing attempt at the Spear T Ranch airstrip (private; elevation 4,340feet), Lewistown, Montana. The commercial pilot, the sole occupant on board, was not injured. The pilot/owner was operating the airplane under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the personal local flight which originated approximately 35 minutes before the accident. The pilot had not filed a flight plan. The pilot said that he taxied the full length of the runway before takeoff, but did not notice the coyote hole. Upon landing, he said he hit something "hard" immediately after touchdown. The pilot performed a go-around, landed, and taxied to the hangar uneventfully. Post impact inspection revealed wrinkled skin under the left door. After removing the seats, it was determined that the carry-thru structure was bent. The pilot said that he had mowed the field two days prior to the accident, and the hole was not there.