Ancestral Rio Grande The
sedimentary basins forming the modern
Rio Grande Valley were not integrated into a single river system draining into the Gulf of Mexico until relatively recent geologic time. Instead, the basins formed by the opening of the
Rio Grande rift were initially
bolsons, with no external drainage and a central
playa. An axial river existed in the Espanola Basin as early as 13 million years ago, reaching the Santo Domingo Basin by 6.9 million years ago. However, at this time, the river drained into a playa in the southern
Albuquerque Basin where it deposited the
Popotosa Formation. The upper reach of this river corresponded to the modern
Rio Chama, but by 5 million years ago, an ancestral Rio Grande draining the eastern
San Juan Mountains had joined the ancestral Rio Chama. Later
Paleo-Indian groups included the
Belen and
Cody cultures, who appear to have taken advantage of the Rio Grande Valley for seasonal migrations and may have settled more permanently in the valley. The Paleo-Indian cultures gave way to the
Archaic Oshara tradition beginning around 5450 BCE. The Oshara began cultivation of
maize between 1750 and 750 BCE, and their settlements became larger and more permanent. This led to decades of conflict (the Coalition Period), the eventual merging of cultures, and the establishment of most of the
Tanoan and
Keresan pueblos of the Rio Grande Valley. This was followed by the Classic Period, from about 1325 CE to 1600 CE and the arrival of the Spanish. The upper Rio Grande Valley was characterized by occasional periods of extreme drought, and the human inhabitants make extensive use of gridded gardens and check dams to stretch the uncertain water supply.
Spanish exploration 's four-sheet map of North America, the first printed map to accurately depict the course of the Rio Grande (named
Rio Escondido) flowing into the
Gulf of Mexico In 1519, a Spanish naval expedition along the northeastern coast of Mexico charted the mouths of several rivers including the Rio Grande. In 1536, the Rio Grande appeared for the first time on a map of
New Spain produced by a royal Spanish cartographer. In the autumn of 1540, a military expedition of the
Viceroyalty of New Spain led by
Francisco Vásquez de Coronado,
Governor of Nueva Galicia, reached the
Tiwa pueblos along the Rio Grande in the future
New Mexico. On July 12, 1598,
Don Juan de Oñate y Salazar established the New Spain colony of
Santa Fe de Nuevo Méjico at the new village of
San Juan de los Caballeros adjacent to the
Ohkay Owingeh Pueblo at the confluence of the Rio Grande and the
Río Chama.
Since 1830 During the late 1830s and early 1840s, the river marked the disputed border between Mexico and the nascent
Republic of Texas; Mexico marked the border at the
Nueces River. The disagreement provided part of the rationale for the
Mexican–American War in 1846, after Texas had been admitted as a new state. Since 1848, the Rio Grande has marked the boundary between Mexico and the United States from the twin cities of
El Paso, Texas, and
Ciudad Juárez, Chihuahua, to the Gulf of Mexico. As such, crossing the river was the escape route used by some Texan
slaves to seek freedom. Mexico had liberal colonization policies and had abolished slavery in 1828. In 1899, after a gradual change to the river position, a channel was dug for flood control which moved the river, creating what was called Cordova Island, which became the center of the
Chamizal dispute. Resolving the dispute took many years and resulted in a
1909 combined assassination attempt on the American and Mexican presidents.
Rio Grande Water Rights (1900–present) Following the approval of the
Rio Grande Project by federal lawmakers in 1905, the waters of the Rio Grande were to be divided between the states of New Mexico and Texas based on their respective amount of irrigable land. The project also accorded of water annually to Mexico in response to the country's demands. This was meant to put an end to the many years of disagreement concerning rights to the river's flow and the construction of a dam and reservoir at various location on the river between the agricultural interests of the
Mesilla Valley and those of
El Paso and
Juárez. In the agreement provisions were made to construct
Elephant Butte dam on public lands. This act was the first occurrence of congressionally directed allocation of an interstate river (although New Mexico would not achieve statehood till 1912). Following the admittance of New Mexico into the union, the increased settlement of the Rio Grande farther north in Colorado and near Albuquerque, the
1938 Rio Grande Compact developed primarily because of the necessary repeal of the Rio Grande embargo among other issues. Though both Colorado and New Mexico were initially eager to begin negotiations, they broke down over whether Texas should be allowed to join
negotiations in 1928, though it had representatives present. In an effort to avoid litigation of the matter in the
Supreme Court a provisional agreement was signed in 1929 which stated that negotiations would resume once a reservoir was built on the New Mexico-Colorado state line. The construction of this was delayed by the
Market Crash of 1929. With negotiations remaining stagnant, Texas sued New Mexico over the issue in 1935, prompting the intervention of the
president who set up the Rio Grande Joint Investigation the findings of which helped lead to the final agreement. The compact remains in effect today, though it has been amended twice. In 1944, the US and Mexico signed a
treaty regarding the river. Due to drought conditions which have prevailed throughout much of the 21st century, calls for a reexamination of this treaty have been made by locals in New Mexico, Mexico, and Texas. Texas, being the state with the least amount of control over the waterway, has routinely seen an under-provision of water since 1992. In 1997, the US designated the Rio Grande as one of the
American Heritage Rivers. Two portions of the Rio Grande are designated
National Wild and Scenic Rivers System, one in northern New Mexico and the other in Texas, at
Big Bend National Park. In mid-2001, a -wide sandbar formed at the mouth of the river, marking the first time in recorded history that the Rio Grande failed to empty into the Gulf of Mexico. The sandbar was
dredged, but reformed almost immediately. Spring rains the following year flushed the reformed sandbar out to sea, but it returned in mid-2002. By late 2003, the river once again reached the Gulf. in 2022. The water of the Rio Grande is over-appropriated: that is, more users for the water exist than water in the river. Because of both drought and overuse, the section from Las Cruces downstream through Ojinaga frequently runs dry and was recently tagged "The Forgotten River" by those wishing to bring attention to the river's deteriorated condition. In 2022, due to increasing drought and water use, the water debt owed to Texas increased from 31,000 acre-feet to over 130,000 acre-feet since 2021, despite "very significant efforts that were done on the river this year to keep water flowing downstream." In response, New Mexico increased its program offering to subsidize farmers who fallow their fields rather than planting crops, which uses additional water; the city of Albuquerque shut off its domestic supply diversion and switched to full groundwater pumping in 2021. Additionally, in 2022, work began on
El Vado Dam, during which it is unavailable for storage, reducing system capacity by about 180,000 acre-feet. MRGCD has requested storage of "native water" downstream at
Abiquiu Reservoir, which normally only stores waters imported into the Rio Grande watershed from the
Colorado River watershed via the
San Juan–Chama Project.
Elephant Butte Reservoir, the main storage reservoir on the Rio Grande, was reported at 13.1% of capacity as of May 1, 2022, further decreasing to only 5.9% full by November 2021. The following winter, the basin experienced above-average snowfall, leading to very high flows in the river in spring of 2023 and flooding of some of its tributaries, including the
Jemez and
Pecos Rivers. By that summer, after the spring runoff had concluded and due to a failed
New Mexico monsoon season and record high temperatures, the river went dry in Albuquerque for a second consecutive year. ==River modifications==