three full days, they still had not been successful, and it is speculated that the Hopi, who probably knew a way down to the canyon floor, were reluctant to lead them there. As a last resort, Cárdenas finally commanded the three lightest and most agile men of his group to climb down by themselves (their names are given as Pablo de Melgosa, Juan Galeras, and an unknown, third soldier). After several hours, the men returned, reporting that they had only made one third of the distance down to the river, and that "what seemed easy from above was not so". Furthermore, they claimed that some of the boulders which they had seen from the rim, and estimated to be about as tall as a man, were in fact bigger than the Great Tower of Seville, at . Cárdenas finally had to give up and returned to the main army. His report of an impassable barrier forestalled further visitation to the area for two hundred years. Only in 1776 did two Spanish Priests, Fathers Francisco Atanasio Domínguez and Silvestre Vélez de Escalante travel along the North Rim again, together with a group of Spanish soldiers, exploring southern Utah in search of a route from Santa Fe, New Mexico to Monterey, California. Also in 1776, Fray Francisco Garces, a Franciscan missionary, spent a week near Havasupai, unsuccessfully attempting to convert a band of Native Americans. He described the canyon as "profound". Americans James Ohio Pattie and a group of American trappers and mountain men were probably the next Europeans to reach the canyon in 1826, although there is little supporting documentation. The signing of the Treaty of Guadalupe Hidalgo in 1848 ceded the Grand Canyon region to the United States. Jules Marcou of the Pacific Railroad Survey made the first geologic observations of the canyon and surrounding area in 1856. Jacob Hamblin (a Mormon missionary) was sent by Brigham Young in the 1850s to locate easy river crossing sites in the canyon. Building good relations with local Native Americans and white settlers, he discovered Lee's Ferry in 1858 and Pierce Ferry (later operated by, and named for, Harrison Pierce)—the only two sites suitable for ferry operation. In 1857 Edward Fitzgerald Beale led an expedition to survey a wagon road from Fort Defiance, Arizona to the Colorado River. On September 19 near present-day National Canyon they came upon what May Humphreys Stacey described