In 1768, he was assigned to the Pacific port of San Blas, in the Viceroyalty of New Spain (present day Mexico), and acquired the rank of ensign (alférez).
In early 1774, the Viceroy of New Spain, Antonio María Bucareli y Ursúa, commanded Pérez to explore the Pacific coast with the objective of reaching 60° north latitude (about the latitude of present-day Cordova, Alaska) to discover possible Russian America and British settlements and to re-assert the long-standing Spanish claim to the Pacific Northwest.
Rumors of Russian fur traders caused the Spanish to send the frigate Santiago north under the command of Pérez, with a crew mostly from New Spain.
Due to a lack of provisions and the poor health of his crew, Pérez turned south at this point despite the viceroy's orders to attain 60° north.
[4] Pérez gave the name of Cerro Nevado de Santa Rosalía ("Snowy Peak of Saint Rosalia") to present day Mount Olympus in the U.S. state of Washington.