The G4 Ranch was one of the largest in the Trans-Pecos in the late 1880s and early 1890s. John T. Gano, the son of former Confederate general Richard M. Gano, arrived in the Big Bend region in 1879; the firm of R. M. Gano and Son of Dallas was one of several land-locating businesses working in conjunction with Presidio County surveyors. John Gano served as deputy surveyor for Presidio County, which at that time still included all the area of present Brewster County. He was sufficiently impressed by the country he saw in the course of his surveying that in 1885 he and his brother Clarence organized the Estado Land and Cattle Company, headquartered in Dallas. They purchased 55,000 acres in survey Block G4 (hence the name of the ranch) and leased other watered sections nearby. They established their ranch headquarters at Oak Spring or Ojo de Chisos, just west of the Basin in what is now Big Bend National Park; established line camps at the mouth of Terlingua Creek and near Agua Fria Mountain; and persuaded James B. Gillett to resign as marshal of El Paso to manage the ranch, which was close to a spread that Gillett and his former Texas Ranger colleague C. L. Nevill had purchased. The ranch extended from Agua Fria Mountain on the north to the Rio Grande on the south, and from Terlingua Creek on the west to the Chisos Mountains on the east; it thus covered most of what is now southwestern Brewster County. This was land that had never been stocked; at the time, recalled Gillett, "The Ganos had it all to themselves." In May 1885 they bought 2,000 cattle in Dallas and Denton counties and shipped them to Toyah, then drove them overland to the G4. They bought 2,000 more in Uvalde and drove them west to the ranch by way of Del Rio, Langtry, Dryden, Sanderson, and Marathon. Other cattle were shipped to Marathon, and by the late summer of 1885 the G4 had a herd of 6,000. The G4 cattle survived the drought of 1886 relatively unscathed because the land on which they were kept had not been overstocked or overgrazed, and in 1891 the herd was estimated at 30,000 head. Nevertheless, dry years and other problems caused the company to disband in 1895. By then the Ganos had driven 15,000 cattle north to Marathon to be shipped to market. They sold the remaining 15,000 to Doc Gourley and Pink Taylor.
In 1929 Homer Wilson, a mining and petroleum engineer from Del Rio, arrived in Brewster County and began buying grazing land west of the Chisos Mountains. He eventually acquired forty-four sections, including most of the old G4, and established his headquarters at Oak Spring. Wilson became the first large-scale sheep and goat rancher in the Big Bend area, where he introduced various ranching and water-conservation innovations. He remained in business until the mid-1940s, when Big Bend National Park took over much of the land that had belonged to the old G4.