On May 31, 1998, about 2000 Alaska daylight time, a tundra tire equipped Piper PA-18 airplane, N4587A, sustained substantial damage when it collided with terrain during a low pass over a potential landing site located about 20 miles northwest of Talkeetna, Alaska. The commercial pilot and the one passenger aboard were not injured. The 14 CFR Part 91 personal flight departed Talkeetna about 1830. Visual meteorological conditions prevailed, and a VFR flight plan was filed. During a telephone conversation with the NTSB investigator-in-charge on June 1, the pilot related he was taking the passenger to scout potential landing sites for a future rafting trip. On one low pass over a ridge top, the pilot said he miscalculated the pitch of the rising terrain. He said the airplane was unable to climb as rapidly as the rising terrain, and collided with a hillside. The pilot indicated there were no preimpact mechanical difficulties with the airplane.