ROCK SPRING. Rock Spring, a natural water hole in a basin formed by the Tordilla Hills in eastern Atascosa County, was a place where travelers, stage passengers, freighters, and livestock could obtain water as they traveled the San Patricio Trail in the mid-nineteenth century. First used by Gen. Zachary Taylor's soldiers in 1845–46, it was the only place between Oakville (Puente Piedra) and Gray's Rancho (Graytown) where there was a sure supply of water. Old-time cowboys called the place the "Jump Off." It was the predecessor to the Tordilla Mound community, which had a post office in 1858–59. The area around the spring was disturbed in the 1970s by quarrying operations to supply crushed rock for Interstate Highway 37 and the railroad track from Campbellton to the San Miguel lignite plant near Christine.