In 1796, he worked for Andrew Ellicott, boundary commissioner for the United States, who was mapping the Missouri River. Governor Gayoso de Lemos was not pleased when Nolan arrived at Natchez accompanied by the surveying party. However, Nolan managed to patch things up, at least with Governor Carondelet in New Orleans, and obtained a third passport to enter Texas, despite the fact that trade directly between Louisiana and Texas was still officially prohibited by Spain. Gayoso de Lemos was not fooled. He wrote directly to the viceroy of Mexico, warning him against foreigners (such as Nolan) who were stirring up the Texas Indians against Spanish rule.