On August 7, 2005, approximately 0945 mountain daylight time, a Stinson L-5G, N2584B, piloted by a commercial pilot, was substantially damaged when it ground looped during landing at Gallup Municipal Airport (GUP), Gallup, New Mexico. Visual meteorological conditions prevailed at the time of the accident. The flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot reported no injuries. The flight originated at Cottonwood, Arizona, approximately 0600, and was en route to Gallup, New Mexico. The pilot said that the winds were calm as he made a three point landing on runway 06. He held full aft elevator as the airplane rolled out, but then it veered left off the side of the runway and into the grass. The pilot added power but the airplane ground looped and nosed down. The pilot said that when he took off from Cottonwood, Arizona, the contents of his flight bag spilled onto the rear floor. He surmised that some of the items may have interfered with the flight controls. Postaccident inspection by an FAA inspector revealed that one of the outer wing spars was broken, the fuselage and cowling showed signs of structural damage, and the outer spar on the left wing was broken.