This Timeline of the Portolá expedition tracks the progress during 1769 and 1770 of the first European exploration of the Spanish possession of Alta California, present-day California, United States. Missionary Juan Crespi kept a diary detailing the group's daily progress and detailed descriptions of their location, allowing modern researchers to reconstruct their journey. Portions of other diaries by Gaspar de Portolá, engineer Miguel Costansó, missionary Junípero Serra, army officer Jose de Canizares, and Sergeant José Ortega also survived. When analyzed as a whole, they provide detailed daily information on the route traveled and camping locations, as well as descriptions of the country and its native inhabitants.
The Portolá expedition was the brainchild of José de Gálvez, visitador (inspector general, a personal representative of the king) in New Spain. On his recommendation, King Charles III of Spain authorized Gálvez to explore Alta California and establish the first permanent Spanish presence there. Gálvez was supported in the planning of an expedition by Carlos Francisco de Croix (Viceroy of New Spain), and Father Junípero Serra (head of the Franciscan mission to the Californias).
Gálvez and Serra met in November, 1768, to plan the expedition. The goals set were to establish two Presidios and nearby missions – at San Diego and Monterrey (one "r" has since been dropped). These places had been described and given names 166 years before by the maritime explorations of Sebastián Vizcaíno. In addition, the name San Carlos Borromeo was chosen for the mission at Monterrey.