On April 30, 1598, during Juan de Oñate’s expedition north from Mexico up the Rio Grande del Norte, he claimed all of that river’s drainage for Spain.  The Adams-Oñis Treaty of 1819 between Spain and the United States more precisely defined, Spanish Territory in present day Colorado as everything south of the Arkansas River and west of a line running due north from the Arkansas River Headwaters on Fremont Pass up to the 102nd parallel. 

Juan de Archuleta led a Spanish excursion into what in now Colorado in 1664. Following an unknown route, he chased runaway Taos Pueblo Indians to El Quartelejo, an Apache settlement on the Arkansas River near present day Las Animas. The first traceable Spanish expedition into Colorado came in 1694 when Diego de Vargas, the governor of New Mexico, followed the Rio Grande to a tributary, Culebra Creek. Vargas skirmished with Ute Indians, marveled at a herd of five hundred buffalo in the San Luis Valley, and left a journal in which he mentioned the names of Colorado rivers, creeks, and mountains, indicating that the Spanish had already explored parts of southern Colorado.

In 1706, Juan de Ulibarrí and forty soldiers traveled north to the Arkansas River, skirting the Spanish Peaks. Like Archuleta, Ulibarrí headed for El Quartelejo, the Apache settlement that had become a haven for Pueblo Indians fleeing Spanish rule. Ulibarrí claimed the Rio Grande and Arkansas drainages for King Philip V of Spain. In officially claiming" "the province of San Luis,"

 Ulibarri's party first sang the Te Deum Laudamus, then he made a speech, cut the air in all four directions with his sword, and presided over a discharge of guns.

Antonio de Valverde, governor of New Mexico, became the next known official visitor in 1719. He crossed the Raton Mountains and headed for El Quartelejo, where he apparently failed to build a planned fort and mission. In the following year Pedro de Villasur set out from Santa Fe with forty-five Spanish soldiers and about sixty Indian allies. Pushing beyond El Quartelejo into unknown territory, Villasur's party explored the South Platte River, which he named the Rio Jesus y Maria. They camped near the junction of the North and South Platte rivers, where Pawnees, encouraged by the French, surprised the camp at dawn, killing Villasur and all but thirteen of his party.

Juan Maria de Rivera became the first recorded explorer of southwestern Colorado in 1765. Rivera skirted the San Juan Mountains and got as far as the Gunnison River near present-day Delta, where his troop carved a cross, a name, and the date into a tree.  Rivera reported finding silver in what are still called the La Plata Mountains.

Hoping for an overland link between her New Mexico settlements and those in California, Spain sought to establish a route between Santa Fe and the West Coast. To this end, two Franciscan priests, Fathers Francisco Atanasio Domínguez and Silvestre Vélez de Escalante, set out from Santa Fe in 1776 for Monterey, the Spanish capital of California.  In their ten-man party was Captain Bernardo y Pacheco Miera, an engineer and artist, who drew the first surviving, detailed map of Colorado [see Figure 1]. In his honor, a particularly spectacular and craggy canyon of the Dolores River was christened El Laberinto de Meira (Meira’s labyrinth) because he found a way through it. The Domínguez -Escalante party followed more or less Rivera's route along or across the Dolores, San Miguel and Uncompahgre rivers to the Gunnison River. Pushing westward into modern Utah, they reached Utah Lake but the approaching winter blizzards and formidable mountain ranges still ahead inspired them to abandon their California goal. They returned to Santa Fe via the Grand Canyon. Escalante's diary and Captain Miera's map made this the most important Spanish expedition into Colorado and gave the world the first detailed map and description of western Colorado.

In 1779 New Mexico Governor Juan Bautista de Anza led 645 men on the last major Spanish thrust into Colorado. Marching through the San Luis Valley and over Poncha Pass, Anza's army then turned east to corner Chief Cuerno Verde (Green Horn) and his Comanches, whom they routed on what is still called Greenhorn Creek. Other Spanish and Mexican expeditions have gone unrecorded in a state that Hispanics were the first Europeans to explore, map, write about and settle.

After winning independence from Spain in 1821, Mexico grew concerned about protecting its northernmost territory, where it faced not only hostile Native Americans, but aggressive United States citizens who had erected Bent's Fort just across the Arkansas River, the border between U.S. territory and Mexico. Toreinforce Mexican claims to what is now part of Colorado; Gov. Manuel Armijo of New Mexico made land grants to attract settlers.

The Tierra Amarilla Grant along the upper Chama River went to Manuel Martinez, his eight sons, and several associates. Most of the area lay in New Mexico, but a small wedge protruded into parts of what became Archuleta and Conejos counties in Colorado.

The Conejos Grant was awarded at the request of citizens of Taos County, New Mexico. The large grant covered much of the western half of the San Luis Valley, including Conejos and Rio Grande counties in Colorado and some of New Mexico. An 1843 attempt to settle on the Conejos River was frustrated by hostile Utes.  Not until 1854 did the town he town of Guadalupe become established.  Later it was absorbed by the town of Conejos just across the Conejos River on higher, less flooded ground.

The Maxwell Grant (also known as the Beaubien and Miranda) was awarded to Charles Beaubien and Guadalupe Miranda. Lucien B. Maxwell, a son‑in‑law of Charles Beaubien, gained control of this vast New Mexico estate, which included a slice of the future Las Animas County in Colorado. This huge grant extended from the crest of the Sangre de Cristo Range eastward for around 50 miles and as far south as Taos, New Mexico.

The grant to Cornelio Vigil and Ceran St. Vrain covered four million acres that stretched from the Sangre de Cristo Mountains on the west to the Purgatoire River on the east, and from the Arkansas River on the north to Trinidad on the south.   Cornelio Vigil was a judge in Taos. Ceran St. Vrain, a trapper and trader born a U.S. citizen in St. Louis, became a naturalized Mexican. Charles Autobees, James Beckwourth, William Bent, Thomas 0. Boggs, Christopher “Kit” Carson, Joseph B. Doyle, Lucien B. Maxwell, and Felix St. Vrain were among the early settlers on the Vigil and St. Vrain Grant, building adobe towns such as Greenhorn (1846), Hardscrabble (1840), and Pueblo (1842).

The Nolan Grant to Gervasio Nolan, a French‑Canadian living in Taos, was made by Governor Armijo a few days after the Vigil and St. Vrain grants. This tract of more than half a million acres stretched from the Arkansas River southwest of Pueblo to the Wet Mountains on the east where it adjoined the Vigil and St. Vrain Grant. Nolan, an illiterate frontiersman, began planting corn on his grant in the 1840s, but he may have been a front man for Cornelio Vigil, who was legally entitled to only one claim.

The Sangre de Cristo Grant, presented by Governor Armijo to Stephen Luis Lee and Narciso Beaubien, stretched from the crest of the Sangre de Cristo range westward to the Rio Grande, embracing all of what is now Costilla County and some of northern New Mexico. Although Lee and Beaubien, two residents of Taos, did not settle on their grant, others did. The town of San Luis, the oldest permanent  town in Colorado, was established there in 1851. San Luis still uses its 1852 communal water ditch and La Vega, a 600‑acre public commons.

The Luis Maria Baca Grant No. 4 in the San Luis Valley was made in 1860 when the U.S. government gave the 100,000‑acre site to the Baca family in exchange for some of the original Baca Grant in New Mexico.

These Mexican land grants suffered various fates after 1848, when Mexico surrendered this territory to the United States in the Treaty of Guadalupe Hidalgo, which ended the Mexican War. Although the treaty guaranteed property rights of Mexican settlers, much land was stripped away from the original owners. Complex and controversial circumstances surrounded the disposition of these vast grants. United States courts cast doubt upon the claims by citing an 1824 Mexican law forbidding government grants larger than eleven square leagues (a square league was about 4,400 acres). All of these Mexican grants were larger than that and thus could be construed as illegal. Under the terms of the original grants, settlement had to take place within a specified number of years or ownership would revert to the government. Thus lack of settlement became another legal cloud.

Many of the original grantees were dead or no longer had written records of their grants by 1891, when the U.S. Congress authorized settlement of the land grant claims by the Court of Private Land Claims. This court threw out the Conejos grant, declaring that the land had not been settled within the time specified by the terms of the grant. The Vigil and St. Vrain grant was reduced from over 4 million acres to 97,390.95 acres in an 1860 U.S. court decision, which was upheld in 1898. The Maxwell, Sangre de Cristo, and Baca claims were upheld, but the Nolan grant was reduced to eleven square leagues (48,700 acres).

 Within the grants, individual settlers struggled to keep smaller lots. Sometimes U.S. courts threw out their claims for lack of written proof of ownership, a formality more important under U.S. than Mexican law. Other Mexican‑American pioneers were able to retain their property, but the land‑grabbing legacy of conquest causes ill feeling to this day.

A century and a half of judicial assaults on Mexican land grants ended on June 24, 2002 when the Colorado Supreme Court ruled, by a four to two vote, that descendants of the original settlers the Sangre de Cristo Grant had the right to the traditional uses of access for grazing, firewood, and timber but not for fishing, hunting, and recreation on the communal land that had become part of the Taylor Ranch.  North Carolina timber baron Jack Taylor purchased 77,500 acres of the Sangre de Cristo Grant in 1960 and fenced off locals pursing traditional grazing, hunting, wood gathering and other communal uses. 

Life changed for Spanish speaking farmers and ranchers after railroads arrived in Colorado in the 1870s.   Along with the railroad came English-speaking settlers who influenced economic and political change.  Poorer Hispanics from the southern part of the state often migrated to work in the northern Colorado mines, in the steel mills of Pueblo, and to work in the sugar beet industry in Larimer County.  Hispanos often served in the U.S. military during the Indian Wars and the Civil War at Glorietta and Valverde.  After returning from World War I and World War II, Hispanic servicemen increasingly moved their families from rural agricultural locations into the larger urban centers of Denver, Pueblo, Greeley and Ft. Collins.  Many moved into neighborhoods such as southwest Denver’s Auraria.

In the 1960s, Chicano rights organizations were founded in Colorado and leaders like Corky Gonzales and Richard Castro emerged bringing a new contemporary Hispanic history to Colorado.  Growing Latino clout led to the elections of Federico Peña as mayor of Denver (1983-1991), Ken Salazar as U. S. Senator (2005-2009) and U.S. Secretary of the Interior (2009- present) and John Salazar as U.S. Representative (2005-2010).

2010 U.S. Census confirms that Hispanics are the largest and one of the fastest growing ethnic groups in Colorado.  Roughly one out of every five Coloradans is Hispanic , one out of every three Denverites, and one out of two residents of the San Luis Valley.  As the first and the largest group on non-natives to settle Colorado, their story is essential to the history of the highest state.