On September 5, 1999, about 1300 hours Pacific daylight time, a Cessna 172N, N733WX, sustained substantial damage during taxi for takeoff at the McClennan-Palomar Airport, Carlsbad, California. Plus One Flyers, Inc., was operating the rental airplane under the provisions of 14 CFR Part 91. The private pilot and two passengers were not injured. Visual meteorological conditions prevailed and no flight plan was filed. The personal flight was bound for Las Vegas, Nevada. The pilot stated the airplane was tied down in an area known as Cinema East. From this location an airplane was required to taxi down a road to gain access to the regular taxiway. He hit an unmarked telephone pole close to the road with the left wing tip. He stated the road was narrow, but had a stripe down its center that jogged to avoid the pole. He shut down the airplane to inspect the damage. He detected a small dent and noted a chipped section of a thick application of what he thought was putty from a previous repair. He also noted the wing end cap was cracked. Since the damage did not look severe, he proceeded to complete his planned round trip to Las Vegas. A subsequent maintenance inspection revealed the wing was displaced aft and the wing spar buckled.