On June 19, 2005, about 0930 Pacific daylight time, a Piper PA-18-135, N2663A, nosed over during an aborted takeoff from an open field about 5 miles west of Pine Valley, California. The airplane was owned and operated by a private individual. The airplane was substantially damaged, and the private pilot was not injured during the personal flight. Visual meteorological conditions prevailed at the time, and no flight plan had been filed. The flight was performed under the provisions of 14 CFR Part 91, and it originated from San Diego, California, about 0900. The pilot reported to the National Transportation Safety Board investigator that he planned to practice touch-and-go landings on the grass-covered pasture in his conventional gear airplane. The pilot made an uneventful landing, and he applied engine power to takeoff. During the takeoff roll as the airplane was approaching the end of the field, the pilot decided to abort the takeoff. He stated, "I hit the brakes too hard," and the airplane nosed over. The pilot reported that no mechanical malfunctions were experienced with his airplane. The pilot subsequently reported that the pasture on which he had landed was sloped downhill.