In the pilot's written statement, he reported speaking with local area pilots prior to going to the accident airport to obtain the general conditions for the airport environment. The local area pilots told him not to land on the first half of the runway due to muddy conditions. Upon arrival, the pilot overflew the airport prior to landing. He noted two parked airplanes, with one of the them parked so that a wing was near the runway. He completed the traffic pattern and landed right after the parked airplanes. He was not able to stop the airplane and it overran the runway and impacted small trees about 50 feet from the end of the runway. The pilot indicated that the airplane and engine had no mechanical failures or malfunctions during the flight. In the remarks section of the Federal Aviation Administration Airport/Facility Directory for Graham United States Forest Service Airport (U45), Atlanta, Idaho, it states that the lower 1/3 of runway 18/36 is soft and unusable during the early spring. The runway is 2,900 feet in length and 50 feet wide.