El Horcon Tract and Rio Rico
Mercedes, Hidalgo County, Texas
Marker Inscription
The Treaty of Guadalupe Hidalgo which ended the Mexican War (1846-48) designated the main channel of the Rio Grande as the Mexico-U.S. boundary. Disputes arising from frequent changes in the river's course led to the Treaty of 1884 which recognized only those river diversions resulting from natural occurences. The International Boundary Commission was established in 1889 to administer the Treaty of 1884. In 1906 the American Rio Grande Land and Irrigation Company dug an unauthorized canal about two miles south of here which altered the natural course of the Rio Grande. As a result, a 419-acre section of U.S. property called El Horcon tract was isolated south of the river. Although still U.S. territory according to the Treaty of 1884, the tract and the popular gambling and resort community of Rio Rico which flourished there during the 1920s and 1930s became increasingly subject to Mexican administration and jurisdiction. After the U.S. granted Mexico territorial rights over El Horcon tract and Rio Rico in 1970, a native of Rio Rico sued the U.S. government to guarantee his U.S. citizenship. This lawsuit began an eight-year legal battle that eventually led to U.S. citizenship for about 200 people born in Rio Rico prior to 1970. (1994)
Erected by Texas Historical Commission
The Story
The 1848 Treaty of Guadalupe Hidalgo fixed the Rio Grande's main channel as the U.S.–Mexico line, but the river's wandering course bred endless disputes. In 1906 an unauthorized canal shifted the Rio Grande and stranded the 419-acre El Horcon tract—home to the freewheeling resort of Rio Rico—on the Mexican side, where it drifted under Mexican control. After the U.S. ceded the tract to Mexico in 1970, a Rio Rico native's lawsuit secured U.S. citizenship for some 200 people born there before the transfer.
Why it matters
This shifting patch of riverbank shows how a line drawn on water could redraw people's nationality, a vivid case of how the U.S.–Mexico border shaped—and unsettled—the citizenship of those living along it.
The story behind this marker
AI contextThe era
In 1848 the Treaty of Guadalupe Hidalgo ended the war between the United States and Mexico. Along this stretch of the border, the treaty made the Rio Grande the dividing line between the two countries. It seemed simple: the boundary would follow the river's main channel.
The trouble was that the Rio Grande does not stay put. In its lower valley, the river winds in looping bends across a flat landscape, and floods regularly cut new channels, leaving old loops stranded. Every time the river moved, questions arose about which country owned the land caught in between.
The Treaty of 1884 tried to settle the matter. It said that when the river moved gradually or naturally, the border would follow, but sudden shifts would not change the boundary. Five years later, in 1889, the two nations created the International Boundary Commission to put the treaty into practice and sort out the many disputes along the river.
Meanwhile, the lower Rio Grande Valley was being transformed. In the early 1900s, irrigation companies dug canals to bring river water to newly cleared farmland, turning the region into a major agricultural area. It was one of those projects that set the story of El Horcon in motion.
People & events
In 1906 the American Rio Grande Land and Irrigation Company dug a canal about two miles south of where this marker stands. The canal was not authorized, and it changed the natural course of the Rio Grande. The river shifted, and a 419-acre piece of land that belonged to the United States ended up on the south side of the river, cut off from the rest of the country.
Under the Treaty of 1884, this land, known as El Horcon tract, was still American territory, because the river's change had not been natural. But geography is powerful. Separated from Texas by the river and easily reached from Mexico, the tract came more and more under Mexican administration in practice.
In the 1920s and 1930s, a community called Rio Rico flourished there as a popular gambling and resort town. Those were the years of Prohibition in the United States, and border towns where people could drink and gamble drew visitors from the American side. Colorful legends about famous gangsters have attached themselves to Rio Rico over the years, but those tales are hard to verify and are best treated as folklore.
In 1970 the United States granted Mexico territorial rights over El Horcon tract and Rio Rico. Then a native of Rio Rico sued the U.S. government, arguing that because he was born on what was then U.S. soil, he was an American citizen. That case launched an eight-year legal battle, and in the end about 200 people born in Rio Rico before 1970 gained U.S. citizenship.
Its place in the American story
El Horcon is a vivid example of a problem that shaped the entire U.S.-Mexico border: what happens when a boundary follows a river that refuses to stay in place. Along the Rio Grande, dozens of small tracts were caught on the wrong side of the river over the years, creating puzzles of ownership and authority for both nations.
The most famous of these disputes was the Chamizal in El Paso, settled by agreement in the 1960s. El Horcon belongs to the same family of stories and shows how the two countries gradually worked out these problems through treaties and the boundary commission rather than conflict.
The Rio Rico story also raises a deeply American question: who is a citizen? The U.S. Constitution grants citizenship to people born on American soil. For the people of Rio Rico, a canal dug by a private company decades earlier had blurred the meaning of that promise. Their eventual recognition shows how a technical matter of geography could reshape people's identities and rights.
Finally, El Horcon reflects the impact of large-scale irrigation, which transformed the lower Rio Grande Valley into one of the country's important farming regions in the twentieth century. The same canals that made the valley bloom could also, quite literally, move a border.
If you visit
Standing at this marker near Mercedes, you are close to the river whose wandering course caused all of this. The lower Rio Grande Valley is flat, green, and laced with irrigation canals, and seeing that landscape helps you understand how a single canal could redirect a river and, with it, an international boundary.
Keep in mind that El Horcon tract and the former Rio Rico are now part of Mexico, on the far side of the river. This is an active border area, so stay on public roads, follow posted signs, and do not try to approach the river or the border directly from this spot.
As you drive through the valley, watch for canals, pumping stations, and the citrus groves and vegetable fields they serve. Those are the descendants of the irrigation boom of the early 1900s that set this story in motion.
This marker makes a thought-provoking stop on a road trip along the lower Rio Grande. Combine it with other sites in the valley that tell the story of the border, the Mexican-American War, and the communities on both sides of the river, and you will come away with a richer sense of how the line between two nations has shaped the lives of people who live along it.
Written by AI to add context, grounded in the marker’s inscription and the historical record. The inscription above is the original, unaltered text.
Own a business near here? Add it to the map.
Related events
- · Treaty of Guadalupe Hidalgo
- · Treaty of 1884
Themes & tags
Nearby & related markers
Longoria Cemetery
Santa Maria, TX
The Longoria family were among the first Spanish colonists to settle the lower Rio Grande in the mid-1700s, helping found communities such as Reynosa and bringing the cattle-ranching techniques of southern Spain to the region. In 1831 Irineo Longoria expanded the family's holdings north of the river, and generations of Longorias ranched, farmed, and built early irrigation works around Santa Maria. This cemetery, holding an estimated 371 graves, was restored by descendants to preserve their heritage.
Temple Beth Israel
Mercedes, TX
During the 1910s, Jewish families across Hidalgo and Cameron Counties gathered to form a small congregation in the Rio Grande Valley, worshipping in rented rooms with lay readers and a visiting student rabbi for the high holy days. In 1935 they built Temple Beth Israel, designed by Weslaco architect Newell Waters, its members serving the region as merchants, jewelers, and newspaper publishers. As nearby McAllen and Harlingen grew, the congregation dwindled and voted to dissolve in 1948, its members joining neighboring temples.
Our Lady of Mercy Catholic Church
Mercedes, TX
After a land company donated ground in 1908, Our Lady of Mercy Catholic Church was dedicated on Hidalgo Street in 1909, gaining its first resident pastor in 1912 and, in 1922, a new brick church under Father Ivor Gourmelen. From 1915 to 1961 the Sisters of Mercy ran a parochial school, and the parish became the mother church for seven other congregations while fostering a dozen missions across Hidalgo and Cameron counties. It stood at the center of Catholic life in the Mercedes area.
Our Lady of Mercy Cemetery
Mercedes, TX
Mercedes was laid out by a land-improvement company in 1907 during the railroad-driven boom that opened the Lower Rio Grande Valley to farming and new towns. At the Oblate order's request the company set aside ground for Our Lady of Mercy Catholic Church, dedicated in 1909, and this adjoining cemetery received its first marked burial that December. With thousands of graves, it became the resting place for townspeople who were not buried on the surrounding private ranches.