Castolon, also known as Santa Helena, was on the Rio Grande in Big Bend National Park, twenty-three miles southwest of Panther Junction in southwestern Brewster County. The first known resident was Cipriano Hernández, a native of Camargo, Chihuahua, who in 1903 bought three sections of land on the American side of the Rio Grande five or six miles downstream from the mouth of Santa Elena Canyon. Hernández, who called the place Santa Helena, irrigated the fertile bottomland and grew wheat, corn, oats, and other grains, which he sold. He also opened the first store in the area.
Hernández's success inspired others to move to the region, and Castolon soon became a center of agricultural activity. Patricio Márquez opened a second store; Agapito Carrasco settled six Mexican families about a mile downstream from Hernández and called his community El Ojito; and Ruperto Chavarria led a larger group of immigrants to the west bank of Alamo Creek, two miles upriver from Castolon, and named the settlement La Coyota. Eventually Castolon and the nearby communities of El Ojito, La Coyota, Terlingua Abaja, and Buenos Aires, five miles downriver, had some 200 or 300 residents, most of whom engaged in subsistence farming. In 1910, at the outbreak of the Mexican Revolution, the inhabitants requested protection from the United States Army. By 1911 a cavalry troop was stationed at Castolon. It was later supplemented by infantry units from Camp Marfa.
In 1914 Hernández sold out to Clyde Buttrill, a prominent rancher in the Rosillos Mountains, and moved to Terlingua Abaja, where he and his son Guadalupe opened a large mercantile business. Buttrill hired James L. Sublett of Sweetwater to grow alfalfa. Sublett may have been the first man to use mechanized farming techniques in the Big Bend region. He installed the area's first pump irrigation system and brought the first wheat-threshing machine into the valley. By February 1916 he had become Buttrill's partner.
In 1918, however, Buttrill sold out and established a new farm two miles upriver from Castolon. He bought a piece of property from brothers Tom and Charlie Metcalf. This spread was known as the Steele Ranch, after prospector L. V. Steele, who inherited it through his marriage to the daughter of a prominent Mexican rancher. Sublett built himself a house atop a small hill, developed an extensive irrigation system along the floodplain, and converted the old Metcalf house into a store, managed by his son-in-law, Fred Spann.
In 1919 the federal government leased four acres near Castolon, intending to construct permanent quarters for a cavalry troop. Camp Santa Helena, as the installation was called, was completed in 1920 but never used. Also in 1919 Wayne Cartledge, whose father was a prominent Austin lawyer and partner of Terlingua mining baron Howard E. Perry, bought the old Sublett-Buttrill place. Cartledge, who had been manager of the Chisos Mining Company store in Terlingua, was as ambitious as Sublett. He set up a partnership called La Harmonía with Perry, opened a new, larger trading post, and in 1921 began commercial cotton farming in the area. At first La Harmonía shipped its cotton to Houston for ginning, but in the spring of 1923 Cartledge bought a cotton gin that became operational in October of that year.
In 1924 he brought in a former shipbuilder named Richard W. Derrick to get the gin working more efficiently. Derrick trained Alvino Ybarra, a Mexican immigrant, to keep the gin running and in 1926 became the first Castolon postmaster. The establishment of the post office also marked the change of the community's name to Castolon, derived from the nearby Cerro Castellan; there was already another post office in Texas called Santa Helena. Cartledge's gin produced 150 to 200 bales of cotton each season, marketed in El Paso and Houston, and between 1923 and 1942 ginned more than 2,000 bales. Though the cotton operation never became a major financial success, it was a steady source of local employment for decades.
Cartledge also introduced fruit trees, hogs, turkeys, and bees to Castolon's agricultural repertoire. He served as middleman for Mexican trappers who supplied him with fox, beaver, wolf, and bobcat fur, and as a wholesale distributor for local producers of candelilla wax. In 1921 the army allowed Cartledge to move his store into the abandoned barracks at Camp Santa Helena. He and his employees lived in the other buildings. In January 1925 the War Department offered for sale all its abandoned military installations along the Rio Grande, including Camp Santa Helena. Cartledge and Perry bought the nine buildings for $1,280 in April 1926. Cartledge moved the headquarters of La Harmonía into the abandoned military camp.
Unfortunately, after 1927 the Castolon cotton industry began to decline. In that year the United States Immigration Service began strictly enforcing immigration laws, a move that interfered with the ready supply of cheap labor from across the Rio Grande. Many Mexican families left Castolon to avoid deportation. Within ten years Perry began to accuse Cartledge of mismanagement, and in 1940 Cartledge dissolved the partnership. In 1942 La Harmonía ceased cotton farming, and Cartledge turned over the management of the Castolon store to his son.
After the establishment of Big Bend National Park in 1944, Castolon's days were numbered. The estimated population declined from twenty-five in the late 1930s to just three by the early 1960s. The post office closed in 1954, and three years later Cartledge finally signed the deed transferring his holdings at Castolon to the National Park Service, though he retained the right to operate the store for three more years. By the mid-1980s the only residents of Castolon were National Park Service employees, although the Castolon store was still open under NPS management and remained a tourist attraction. In 2000 the population was eight.