TORDILLA HILL. Tordilla (Tordillo) Hill, the highest and most prominent hill in an area of flat-topped hills in northwestern Karnes County (at 28°52' N, 98°09' W), was well-known to early day travelers of the San Patricio Trail and later to geologists. This hill lies in a graben structure formed by the Fashing and Falls City geological faults. With an elevation of 525 feet, it was a landmark that could be seen many miles away by travelers. Rock Spring, a sure supply of water, and the post office called Tordilla Mound were at its base. During World War II an airplane beacon was built on its crown. Areas of anomalous radioactivity and surface exposures of uranium minerals near Tordilla Hill were discovered in 1954. The initial confirmation of uranium ore in commercial quantities was followed by a period of intense exploration activity by major oil companies and individual operators, which lasted until the summer of 1956. One of the first commercial uranium mines in Texas was dug at the base of Tordilla Hill.