With the large-scale mining of coal in Webb County in the latter part of nineteenth century, four mining towns, Santo Tomas, Minera, Dolores (San Jose), and Darwin (Cannel), jointly known as "Las Minas," developed upriver from Laredo. Minera was located on the banks of the Rio Grande about two miles upriver from what is today the Laredo-Colombia Solidarity Bridge, some twenty-five miles northwest of Laredo. It is probably the same community as the one that in 1887 was known as Carbon, which then had a population of 600. Minera was different from the other mining communities in that the miners in Minera dug horizontal shafts or drift mines near the banks of the Rio Grande, whereas most of the other mines in the vicinity were vertical shafts. The majority of people who lived in this mining community were immigrants from northern Mexico, especially from the states of Coahuila, San Luis Potosí, and Durango. Many of the immigrants were experienced miners who had worked the coal and silver mines of Mexico. Although the existence of coal along the Rio Grande has been known about since the colonial era, the first written reports of coal in this area came in 1834 from the Rio Grande and Texas Land Company. Later in 1873, Charles Callaghan, a prominent sheep rancher, and Refugio Benavides, mayor of Laredo, started mining surface outcroppings of coal here. With an abundance of coal, mining operations were expanded. After a thorough reconnaissance of the area by David Darwin Davies in 1880, a serious exploitation of coal was begun. At Davies's urging, Alexander Cameron Hunt, former governor of Colorado, was encouraged to begin large-scale coal mining. Coal was transported to Laredo either by steam-driven river barges or overland in large wagons drawn by twelve mules. The building of the narrow-gauge Rio Grande and Pecos Valley Railroad was completed to Minera in 1882. Hunt's original goal was to push the Rio Grande and Pecos Railroad upriver from Laredo to Eagle Pass to eventually join the Southern Pacific Railroad at the mouth of the Pecos River.
By 1900 Minera had a population of 1,022. Most of the miners were young men in their twenties and thirties. The town also included barbers, farm laborers, carpenters, blacksmiths, shoemakers, and a physician. Women listed their occupation as dressmakers, cooks, schoolteachers, and housekeepers. Although a large percentage of children in Minera were born in Texas, their parents were from Mexico. Many of the children started school at the age of six and continued until they were thirteen. At Minera miners labored for small wages under dangerous conditions. Mining was a dangerous occupation, but it was one of the few jobs available at the time for Mexican immigrants. The 1900 census indicates the literacy rate in Minera at about 70 percent. Most of the miners rented company-owned, small, two-room frame houses. The front room was the living area and the back room was the kitchen and dining room. The houses did not have electricity, provided little warmth in the winter, and were hot during the summer. In 1900 yellow fever struck the town and killed many of the miners, who lived in a low area near the river. In November 1910 Francisco I. Madero went to Minera to buy rifles and ammunition for his planned revolt against Mexican president Porfirio Díaz. About 1912 the shafts at Minera were flooded by the Rio Grande and mining operations were moved inland. By 1915 the population had declined to about 450. Later that year the post office was moved from Minera to Santo Tomas. Today nothing is left of Minera but a giant slag heap of eroded clay and abandoned mine shafts.