On November 06, 2002, at approximately 1400 mountain standard time, a Piper PA-28RT, N2904C, operated by Kempton Air Service of Grand Junction, Colorado, was substantially damaged when its left main landing gear collapsed during landing roll at Walker Field Airport (GJT), Grand Junction, Colorado. The private pilot, the sole occupant on board, was not injured. Visual meteorological conditions prevailed. This personal cross-country flight was being conducted under Title 14, CFR Part 91, and no flight plan had been filed. The flight originated at Durango, Colorado, at approximately 1315. According to the pilot, approximately 35 miles southeast of Grand Junction, the airplane's alternator failed and all electrical power was lost. Attempts to restore electrical power were unsuccessful. While over Whitewater, Colorado, the pilot used his cell phone to call GJT Tower and he was given clearance to land. He followed the airplane's emergency checklist to manually lower the landing gear and landed the airplane on runway 29. During the landing roll, the airplane's left main landing gear collapsed, the airplane veered off the runway and struck the A6 taxiway sign. The airplane's left wing was displaced from the fuselage at the forward attachment fitting and the outboard 5 feet of its leading edge was crushed.