First expedition to give detailed descriptions of Texas' offshore islands and to refer to Corpus Christi Bay by its present name.
The exploration was ordered by the viceroy of New Spain in the midst of rumors that the English planned to encroach on Spanish territory. Parrilla, who had fought the Moors for Spain before holding positions of civil and military leadership in the New World, was ordered to expel any intruders.
He began his trek at San Juan Bautista on the Rio Grande, September 13, 1766. At Corpus Christi Bay a detachment marched south to explore the coastal islands. Their report of uniformly bleak, treeless, waterless dunes (including this area) cast doubt on the feasibility of enemy occupation.
At this point, torrential rains and floods impeded the party's progress. At La Bahia (present Matagorda Bay) Parrilla was luckily able to interview some of the soldiers serving along the coast and thus he obtained knowledge of the geography of the area and its Indians as far north as Trinity Bay.
After several months Parrilla returned, having helped disprove rumors of the English intrusion and bearing vital information on the Texas Gulf Coast.