The pilot reported that while taxiing to the active runway, about 50 yards ahead, he saw what appeared to be a black oval, 4-5 feet in diameter on the taxiway. He stated that he believed it was a wet spot or an area of new pavement, and started to steer around it. As the pilot approached the spot, he reported that he glanced off to the left and saw sink holes in the field, then he looked back towards the taxiway and suddenly the airplane sank into the taxiway. The airplane came to a stop after the right wheel fell into the sink hole and the fuselage impacted the taxiway surface. The hole had opened up to about 9-10 feet across and 7-8 feet deep. The fuselage was substantially damaged in the accident. During a postaccident interview, the airport manager stated that she was unaware of sink holes on any safety areas at the airport, including this taxiway. After the accident, the airport immediately issued a notice to airmen closing the taxiway. The pilot stated there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation.