Juan Domínguez de Mendoza was born in 1631 and went to New Mexico at age twelve. In 1654 he accompanied the expedition of Diego de Guadalajara from Santa Fe to the juncture of the three branches of the Concho River near the site of present San Angelo. Few details of the expedition are known. On expeditions from Santa Fe and El Paso del Norte in 1654 and 1683–84, Domínguez de Mendoza probably saw more of the Texas plains than any previous Spanish explorer.
As lieutenant general and maestre de campo in New Mexico, he played a prominent part in countering the Pueblo Indian revolt of 1680 (in New Mexico) before the Spaniards finally were forced to withdraw to the El Paso area. In 1681 a group of Indian chiefs led by the Jumano Juan Sabeata came to the Paso del Norte settlement requesting the Spaniards to establish missions among the Jumanos. Governor Domingo Jironza Petriz de Cruzate responded by sending Domínguez and Fray Nicolás López to Jumano country to explore, found missions, and establish trade.
The expedition left the El Paso area on December 15, 1683, to descend the Río Grande to La Junta de los Ríos, near the site of present Presidio, Texas. Leaving Fray Antonio de Acevedo in charge of new missions there, fathers López and Juan de Zavaleta continued with Domínguez de Mendoza on a journey that extended beyond the Pecos River to the Edwards Plateau. There, on a river that Domínguez called "the glorious San Clemente," the Spaniards spent six weeks. They built a bastion for protection against Apaches and hunted buffalo for the hides, as well as to feed the thousands of friendly natives who surrounded the camp. The two priests baptized many of the Indians.
Both the location of San Clemente and the route that Domínguez took to reach it have long been the subject of controversy. As early as 1908 Herbert Eugene Bolton theorized that the San Clemente encampment was on the Colorado River above the site of present Ballinger. Carlos E. Castañeda, reviewing the matter in 1936, conjectured a different route to place San Clemente at the juncture of the Concho and Colorado rivers. The Texas Centennial Commission in 1936 recognized Castañeda's choice with a historical marker. More recent studies have disagreed with both Bolton and Castañeda. Jesse W. Williams sought in 1962 to redefine the route but relied on Bolton's translation of the itinerary. He placed San Clemente on the South Llano River not far from the site of present Telegraph.
The various studies, while favoring divergent routes, agree that the expedition reached the point at which the three Conchos come together. The most recent version, inspired by the discovery of ruins thought possibly to be of the bastion that Domínguez built at San Clemente, is that of Seymour V. Connor (1969). Intrigued by the stone remains on the San Saba River eighteen miles west of Menard, Connor has made the most thorough, and evidently the most scientific, route study of all, alleging "serious errors" by each of the three previous interpreters. He claims to have spent "countless hours" poring over topographic maps; to have driven hundreds of miles "to view on the ground every conceivable point that might fit Mendoza's descriptions of the various campsites"; and to have surveyed the area from the air. After reaching the Pecos near Girvin, Connor suggests, the expedition traveled downstream some distance, traversed the corners of Crockett and Upton counties, and passed through Reagan and Irion counties, to reach the confluence of the Conchos in Tom Green County; thence southeast across the northeastern corner of Schleicher County to the place of the rock ruin on the San Saba River, six miles east of Fort McKavett in Menard County. The return route he describes proceeded southeast into Sutton County and thence west across Crockett County to the Pecos.
Excavation supervised by archeologists Earl Green and Curtis Tunnell failed to produce evidence to support Connor's conclusion-not even a buffalo bone. "Never in the experience of the archaeologists on the dig," Connor admits, "have they seen a site of such obvious human construction so devoid of human remains and artifacts." He attributes the lack of artifacts to the shortness of the occupation.
Obviously, the huge rocks of the Menard County ruin indicate that the builder had a considerable labor force at his disposal. Domínguez de Mendoza, Connor points out, had such a force. But so did San Luis de las Amarillas Presidio (San Sabá), at the site of present Menard, which maintained a horse pasture "five leagues" west of the fort. Connor does not consider the possibility that the stone ruins may represent a bastion for the protection of soldiers sent to guard the horses.
Domínguez and López returned to Paso del Norte full of hope for establishing missions, and even a colony, among the Jumanos of the Texas plains. The spreading Indian revolt, however, continued to sap Governor Petriz de Cruzate's resources. Not easily discouraged, the explorers journeyed to Mexico City to urge the Jumano settlement as a barrier against the Apache onslaught. A combination of factors doomed their proposal: the revolt raging across the northern frontier and the invasion of Spanish territory by the Frenchman La Salle, who had landed at Matagorda Bay early in 1685. La Salle caused a shift of the missionary focus from western Texas to eastern.