I found this story on @HistoryWeird's blog here. The original source was The San Francisco Herald, July 24, 1851.
"In the summer of 1851 a military depot at Benicia, California reported being hit by a bizarre thunderstorm. According to eyewitnesses, pieces of raw meat rained from the sky for around three minutes. When the deluge subsided, five acres of the base had been carpeted with small chunks of flesh, origin unknown. According to one San Francisco press report:
"'The pieces were from the size of a pigeon’s egg up to that of an orange, the heaviest weighing three ounces. No birds were visible in the air at the time. Specimens of the meat, which is apparently beef, were preserved by Major Allen and the Surgeon of the Post. A piece that was examined three hours after it fell showed a portion of a small blood vessel, some of the sheath of a muscle and muscle fibre.'
"Any thoughts of hosting California’s largest barbecue were quickly dispelled when the meat turned out to be 'slightly tainted'. The ‘meat shower’ in Benicia wasn’t the only incident of its kind in 19th century California. Small pieces of flesh reportedly fell in Sacramento (March 1863), Los Nietos (August 1869), Juapa (September 1870) and near Los Angeles (August 1871). These later showers also deposited blood, brains, other organs and bone fragments. Experts could provide no adequate explanation for this gory precipitation. Two of the most popular theories were that a tornado had hit a slaughterhouse or offal pit and lifted its contents into the troposphere – or that these towns had been hit by passing flock of vomiting vultures."