For more than 10 years, genealogist Tim Pinnick has devoted himself to an underground project: researching the lives of African-American coal miners. As his efforts gain critical momentum, all the men he's studying seem to be coming to the surface.

Starting with his own ancestors, Pinnick began compiling names of black coal miners in the early 1990s. The more miners he uncovers, the more keep turning up. One big reason for the information explosion is the California Slavery Era Insurance Registry <www.insurance.ca.gov/0100-consumers/0300-public-programs>. A few of today's largest insurance companies still have records of slaveholders' policies, purchased to offset the potential financial loss a slave's injury or death would cause. Since 2001, California legislation has required insurers operating in the state to report that information. Most of it was released in 2002, and Pinnick estimates miners account for 20 percent of the records.