On October 4, 1995, approximately 1200 mountain daylight time, N70221, a Cessna A185E, sustained substantial damage when it dragged a wing during takeoff at a private airstrip near Ola, Idaho. The airline transport pilot, the sole occupant, was uninjured. There was no flight plan for the flight, and the ELT did not actuate. The pilot continued to Boise, Idaho, which was his destination. Although he was aware of damage to the aircraft, the pilot elected to overfly Emmett, Idaho, due to lack of emergency services. He continued to Boise, where he declared an emergency, and reported having control difficulties prior to landing at Boise. He landed with a flat main landing gear tire. An FAA inspector inspected the aircraft and stated that the right aileron was hanging down about 60 degrees, and a spar in the outboard portion of the wing was damaged. The pilot stated that during the takeoff roll, about the time the tail would normally come off the ground, the tail was abruptly swung to the right and the airplane started a skidding left turn that could not be arrested with full right rudder and brake. The pilot elected to continue his takeoff due to speed and braking constraints. The aircraft continued to the left for about 200 feet in an uncontrolled left skid, then very suddenly swung to the right. The pilot stated that the right wing hit the ground at that time. The pilot recovered and became airborne, and noted damage to the right wing and aileron. He elected to continue on to Boise as the aircraft appeared to be controllable and he wished to land where emergency equipment was available. After landing at Boise, the pilot later returned to Ola, where he found a boulder, about the size of a football, on the runway, immediately preceeding skid marks to the left. He believed the tailwheel struck the rock, unlocking the tailwheel, and causing the original directional excursion.