On June 9, 2001, at 1100 hours Pacific daylight time, a Mooney M20J, N4235H, ground looped on the landing roll out from runway 19 at the Westover Field Amador County Airport, Jackson, California. The airplane was operated by the owner/pilot under the provisions of 14 CFR Part 91, and sustained substantial damage. The private pilot and a pilot rated passenger were not injured. Visual meteorological conditions prevailed for the local area flight that departed at 1000. A flight plan had not been filed. The flight was scheduled to terminate at the Westover airport. The Safety Board investigator interviewed the pilot. The pilot stated that the landing was a little too fast. After touchdown the airplane started to porpoise down the runway. A crosswind pushed the airplane to the left of the runway. The left wheel caught on the side of the runway, the airplane ground looped, spun around, and came to rest on its main landing gear. In the pilot's written statement to the Safety Board, he stated that the purpose of the flight was a round robin to three other airports. He departed from Westover at 1000, and stopped at the Calaveras County airport (0O3), the Columbia airport (O22), and the Pine Mountain Lake airport (Q68), all located in California. He departed from Q68 at 1045 and flew direct to Westover. The pilot reported that Westover airport is located on top of a hill and runway 19 has a significant upslope. He entered the pattern on the 45 for a left downwind for landing. After he turned on final approach, he observed the windsock indicating a crosswind, and felt the right to left drift of the airplane. The pilot slowed the airplane to 80 knots for the approach and made the crosswind correction. He stated that he did not pay "sufficient attention to slowing the airplane over the threshold which should have been 70 knots." The airplane landed hard about 400 feet from the approach threshold. The pilot estimated his airspeed to be about 75 knots. The airplane porpoised two times down the runway. He added power to attempt to straighten, and maintain control of the airplane. The pilot stated that two things happened simultaneously; his passenger started yelling which distracted him, and the crosswind pushed the airplane to the left of centerline towards the runway edge. The left main gear departed the runway surface and the airplane departed the runway. After traveling approximately 500 feet from the runway the airplane came to rest in a shallow landfill embankment. He stated there were no discrepancies noted with the round robin flight.