The land of California existed as a myth among European explorers before it was discovered. The earliest known mention of the idea of California was in the 1510 romance novel Las Sergas de Esplandián by Spanish author Garci Rodríguez de Montalvo. The book described the Island of California as being west of the Indies, "very close to the side of the Terrestrial Paradise; and it is peopled by black women, without any man among them, for they live in the manner of Amazons".
Following Hernán Cortés' conquest of Mexico, the lure of an earthly paradise as well as the search for the fabled Strait of Anián, helped motivate him to send several expeditions to the west coast of New Spain in the 1530s and early 1540s. Its first expedition reached the Gulf of California and California, and proved the Island of California was in fact a peninsula. Nevertheless, the idea of the island persisted for well over a century and was included in many maps. The Spaniards gave the name Las Californias to the peninsula and lands to the north, including both Baja California and Alta California, the region that became parts of the present-day U.S. states of California, Nevada, Utah, Arizona, and parts of Colorado and Wyoming.
- 1532: Hernán Cortés sends three ships north along the coast of Mexico in search of the Island of California. The three ships disappear without a trace.
- 1533: Cortés sends a follow-up mission to search for the lost ships. Pilot Fortún Ximénez leads a mutiny and founds a settlement in the Bay of La Paz before being killed.
- 1539: Francisco de Ulloa explores both coasts.
- 1622: A map by Michiel Colijn of Amsterdam showed California as a peninsula rather than an island. Previous maps show the Gulf terminating in its correct location.
- 1690s–1800s: Spanish settlement and colonization in lower Las Californias (Baja California peninsula), the first Spanish missions in Baja California are established by Jesuit missionaries.
- 1701: Explorations by Eusebio Kino expanded knowledge of the Gulf of California coast. Kino did not believe California was an island.
- 1767: Jesuits expelled; Franciscans take over the Baja missions.
- 1769: Franciscans go with the Portola expedition to establish new missions in Alta California. Control of the existing Baja missions passes to the Dominican Order.
- 1773: Francisco Palóu's line demarcates Franciscan and Dominican areas of mission control.
- 1804: Las Californias divided into Alta ("Upper") and Baja ("Lower") California, using Palóu's line.
- 1810–1821: Mexican War of Independence
- 1821: First Mexican Empire, Baja California Territory established, covering Baja California Peninsula.
- 1847: The Battle of La Paz and the Siege of La Paz occurs, as well as several other engagements.
- 1848: Treaty of Guadalupe Hidalgo cedes Alta California to the United States. As a U.S. territory it receives the California Gold Rush, causing increased maritime traffic along the peninsula.
- 1850: California admitted to U.S. statehood.
- 1853: William Walker, with 45 men, captures the capital city of La Paz and declares himself President of the Republic of Lower California. Mexico forces him to retreat a few months later.
- 1930–31: The Territory of Baja California is further divided into Northern and Southern territories (North Territory of Baja California and South Territory of Baja California).
- 1952: The North Territory of Baja California becomes the 29th State of Mexico, Baja California. The southern portion, below 28°N, remains a federally administered territory.
- 1973: The 1,700 km (1,100 mi) long Trans-Peninsular Highway (Mexican Federal Highway 1), is finished. It is the first paved road that spans the entire peninsula. The highway was built by the Mexican government to improve Baja California's economy and increase tourism.
- 1974: The South Territory of Baja California becomes the 31st state, Baja California Sur.