The pilot stated the accident flight departed KPCM at about 12:30 local time. After about an hour of local flight, which included several landings and take-offs from a local grass strip (Blackwater Creek), we flew to my private airstrip, OFL6. We made a normal STOL approach at 50 mph and with 2 notches of flap. There was a slight quartering tail wind from the right. We made a reasonably firm arrival on the main gear as usual. The nose dropped as expected, but then continued to drop so that the propeller impacted the ground. There was no sensation of the nose gear touching the ground and then failing; the nose simply dropped through the normal landing attitude as if the nose gear were not there. After the propeller contacted the ground, the aircraft very slowly nosed over and came to rest on its back. I undid the 4 point harness and exited through the left door, and went around to the other side to help the passenger out. There were no injuries. Post-accident examination of the wreckage revealed that the nose wheel (which is directly linked to the rudder pedals for ground steering) was about 45 degrees to the left. The forks which hold the nose wheel were deformed in a way that suggest that the nose wheel contacted the ground while turned to the left. It is possible that if the nose wheel had been straight when it contacted the ground, then the nose gear would not have been subjected to such high rearward loads, and might not have collapsed.