OK, they’re not really mudballs. The rounded rocks shown below were collected on the Carrizo Plains in San Luis Obispo County between 1954 and 1957 by the current owner’s father. The vast majority of these balls are composed of 20 million-year-old sandstone and a few appear to be granitic in nature. One theory as to their round shape postulates that the rough boulders were transported down a stream into the former ocean and were gradually rounded into their present ball-like configuration. The sizes range from about 5 inches in diameter to about 14 inches in diameter. Many larger balls more than two feet in diameter were left in situ due to their weight. This is a fantastic collection.