Domestic pigs were introduced from Europe to the Americas by Spanish explorers. Over time, some pigs escaped or were intentionally released into the wild. Subsequently, free-ranging, feral populations established themselves on American soil. In 1893, 50 feral pigs from Germany's Black Forest were released on a hunting preserve in New Hampshire's Blue Mountains. Later, in 1910 and 1912, Russian wild boars were released on a North Carolina preserve near the Tennessee border. Russian wild boars were released again in 1925 near Monterey, California and a few years later on Santa Cruz Island. Some of these transplants escaped from the hunting preserves. Many of their offspring bred with feral descendants of domestic pigs. Today, feral pigs and hybrids of the Russian wild boars are found in 23 states with the possibility of yet-undiscovered populations in several more states. The largest populations are in the coastal states surrounding the Gulf of Mexico and California (not surprising, since Spanish explorers settled these territories). Feral pigs are found chiefly in western North Carolina, eastern Tennessee, West Virginia and, in California, on Santa Cruz Island and Monterey and San Luis Obispo counties. Small numbers of pigs are found in New Hampshire, Pennsylvania and Vermont, Alabama, Arizona, Arkansas, Georgia, Florida, Louisiana, Oklahoma, Oregon, South Carolina and Texas. In locations where feral pigs have more recently been discovered it is likely that these "run-wild" individuals are the result of unintentional escapes from domestic swine facilities, escapes or releases from game farms, or illegal stocking. Biologists estimate the nationwide population of feral pigs to be around four million animals.