An expedition seeking a site for an Apache mission in 1753 led to the discovery of Los Almagres Mine in what is now Llano County. Traversing the Central Mineral Region, Lt. Juan Galván heard from Indians of a cerro de almagre, a hill of red ocher, indicating the presence of mineral-bearing ores. Upon Galván's return to San Antonio, several men from that settlement were guided to the hill by Apache Indians in August 1753. No valuable ore was found, but interest in the hill containing gossan refused to die. Governor Jacinto de Barrios y Jáuregui, fearful that the use of Apache guides by unauthorized prospectors would arouse the Comanches, decided to send an official expedition. To lead it, he chose Bernardo de Miranda y Flores, who left San Antonio with twenty-three soldiers and citizens on February 17, 1756.
After locating the cerro de almagre (now known as the Riley Mountains, a quarter league from Honey Creek), Miranda's men opened a shaft and found "a tremendous stratum of ore." They named the mine San José del Alcazar. So abundant were the ore veins, Miranda reported, that he guaranteed "a mine to each of the inhabitants of the province of Texas." Following Miranda's return to San Antonio on March 10, Barrios sent a three-pound ore sample to the viceroy in Mexico City for assay, but the sample was deemed too small for accurate analysis. The assayer suggested that thirty mule-loads of the material be sent to Mazapil for further testing. Miranda sought a subsidy for extracting the thirty cargas of ore and a presidio at the site, with himself as captain, to protect the workers. His bid was not successful.
In the meantime, the Apache mission and a presidio were established on the San Saba River near the site of present-day Menard. The presidio captain, Diego Ortiz Parrilla, seeking permission to move his garrison to Los Almagres to work the mine, obtained ore samples and smelted them at his post. He calculated a yield of 1½ ounces of silver from seventy-five pounds of ore. After destruction of the San Sabá Mission by hostile Indians in March 1758, Ortiz Parrilla was reassigned. The mine was never officially opened. Parrilla's interest, combined with Miranda's report, gave birth to an enduring legend. The slag heap the Spaniards left on the bank of the San Saba River when the presidio was abandoned a decade later fired the imagination of later treasure seekers, who supposed the mine to be in that area.
Interest in the mines continued to surface from time to time throughout the colonial period. Fray Diego Jiménez and Capt. Felipe de Rábago y Terán, Ortiz Parrilla's successor at San Sabá, proposed reestablishing the San Sabá Mission on the Llano River, so that the mineral veins might be worked. The Barón de Ripperdá, as governor, sent an expedition to examine the mines in 1778; ore samples were extracted and sent to the commandant-general of the Provincias Internas, Teodoro de Croix. In 1788–79 a French sojourner, Alexandre Dupont, extracted ore samples from the site and took them to Mexico for assay. He never returned. On the heels of his last visit, six prospectors from San Antonio were attacked at Los Almagres by Apaches. All but one were slain. Indian hostilities thereafter put a damper on such activity.
Stephen F. Austin, on his first trip to Texas, heard from Erasmo Seguín that there was a rich silver mine on the San Saba River and a gold mine on the Llano. Hearing again in Mexico City of the unworked ore deposit called Los Almagres "in the territory of Sansava," he sent soldiers to inspect it. They probably went to the wrong place. In 1829 the mythical "lost" silver mine of San Sabá began appearing on Austin's maps. A year later, Henry S. Tanner borrowed Austin's designation for his own famous Texas map. Its wide distribution resulted in "a rash of maps showing silver mines near the old Spanish fort." Austin, doubtless realizing the value of the legend in attracting immigrants, repeated it in an 1831 promotional pamphlet. For years afterward it was mentioned in nearly every book about Texas.
James and Rezin Bowie, on their sallies into the Hill Country, reinforced the legend. Los Almagres was transformed into the "lost San Saba mine," then the "lost Bowie mine." After 1895 some prankster (presumably) appended the word mine to the Bowie name on the presidio's stone gatepost at Menard. Today, the legend is the focus of an annual Menard festival called Jim Bowie Days, which, like Austin's pamphlet, has a promotional intent. The fact is that the Los Almagres mine that inspired the legend was at another location more than seventy miles away.
In 1842 two Anglo-Texans found the old Spanish diggings on the cerro de almagre but associated them with neither the nearby Arroyo de los Almagres (Honey Creek) nor the legendary San Sabá mine. After the name Almagres was brought forth in a translation of Antonio Bonilla's summary of Texas history in 1904, Herbert E. Bolton obtained a copy of Miranda's journal from a Mexican archive. Miranda's route description led Bolton, accompanied by J. Farley of Dallas, to what had become known as the Boyd shaft on Honey Creek. Farley formed the Los Almagres Mining Company. In 1909 members of the United States Geological Survey visited the site, which they entered on a geologic map of Llano County. They described the mine as being unproductive. Bolton's claim of having found the lost San Sabá mine has not deterred the romantics. Among those who prefer an imaginative tale to historical fact, the search for the mythical lode goes on-in a region of non-mineral-bearing limestone. Fortunes and lives have been wasted in chasing the chimera. Ortiz Parrilla's slag heap left by the old presidio, coupled with Bolton's discovery, emphasizes the futility of their quest.