The set of stamps was issued to commemorate both the discovery of the Pacific Ocean in 1513 and the opening of the Panama Canal in 1914, as well as to publicize the Panama-Pacific Exposition in San Francisco in 1915. San Francisco Bay, with its "Golden Gate" entryway, is said to have been sighted by Sir Francis Drake in 1579, and the city's site was discovered in 1770 by Don Gaspar de Portola, Spanish governor of the Californias. He, with Franciscan missionary Junipero Serra, led a thousand-mile march, establishing settlements from Lower California to Monterey.