The Llanos-Cárdenas Expedition was a follow-up to Alonso De León's 1689 discovery of the remains of La Salle's Texas Settlement, built by René Robert Cavelier, Sieur de La Salle. The expedition sailed from Veracruz on October 12, 1690, to reconnoiter the La Salle's Texas Settlement site (on Garcitas Creek near the head of Lavaca Bay in what is now Victoria County) and to map its environs. Francisco de Llanos, captain of the frigate Nuestra Señora de la Encarnación of the Armada de Barlovento, was in overall command of the expedition. This voyage to the Texas coast, says Herbert E. Bolton, was "of first importance in fixing the location of La Salle's colony."
The 1690 voyage to Espíritu Santo Bay (also known as San Bernardo or Matagorda Bay) was prompted by De León's report of having seen, some distance from shore at the mouth of the Río de San Marcos (now the Lavaca River), two objects that looked like buoys or channel markers. Llanos's first duty was to see that the "buoys" were removed, as it was feared that they might mark the entrance to a river that would afford access to the newly founded San Francisco de los Tejas Mission. Llanos and his crew were to seek a water approach to the new mission, map Espíritu Santo Bay, and determine the suitability of La Salle's Texas Settlement site as the location for a future Spanish presidio. The expedition personnel were carefully selected with those specific purposes in mind. Juan de Triana, chosen by the viceroy for his expertise in Gulf of Mexico navigation, was sent as pilot. For security, Llanos was given a force of soldiers headed by Gregorio de Salinas Varona, who had accompanied the 1689 De León entrada. Assigned as mapmaker was the engineer Manuel José de Cárdenas y Magaña, who had been involved in building fortifications at San Juan de Ulúa; he was qualified both to appraise the strategic possibilities of La Salle's Texas Settlement site and to map the environs.
The Encarnación, provisioned for a three-month voyage, sailed from Veracruz on October 12, 1690. The frigate paused along the way only to sound the mouth of the Rio Grande and on October 24 anchored off Cavallo Pass, the natural entrance to Matagorda Bay. With the sounding of the pass, Cárdenas began to map the bay. Llanos, Cárdenas, and the pilots reached Sand Point by October 30 and proceeded on November 1 into Lavaca Bay, which they named Lago de Todos Santos, for All Saints' Day. They found and removed De León's "buoys," which turned out to be nothing more than upended logs. The explorers then ascended Garcitas Creek (which they called Arroyo de los Franceses) to La Salle's Texas Settlement site (Pueblo de los Franceses), where the French artillery that De León had buried the previous year was examined and then was left where it lay. The mapping expedition traveled also into Chocolate, Cox, and Keller bays and up the Lavaca River to the Navidad fork, before returning to Matagorda Bay proper to examine Tres Palacios Bay and to ascend the Colorado River. Neither the Lavaca nor the Colorado, it was determined, offered a water route to Mission San Francisco. The Llanos-Cárdenas expedition set sail for Veracruz on November 29, 1690, to reach the home port ten days later. Cárdenas's map reflects the reconnaissance in detail, providing reason for Bolton to claim it as proof of the location of La Salle's Texas Settlement. See also SPANISH TEXAS.