1915-S $50 Panama-Pacific 50 Dollar Octagonal MS63 PCGS. A lovely handbook that is widely available to tourists in San Francisco is San Francisco's Panama-Pacific International Exposition 1915, issued by the Golden Gate National Parks Conservancy. With historic hand-tinted photographs of the exposition, which it calls "The Last Great World's Fair," and an introduction by Hallie Brignall, the slim volume brings to life the monumental dual celebration of the Panama Canal completion and the discovery of the Pacific Ocean four centuries earlier by the Spanish explorer Vasco Núñez de Balboa.
The book places the Exposition in its cultural context thus:

"An astonishing achievement, the Exposition brought together the most celebrated architects, artists, and innovators of the time to create a magical vision the likes of which the world had never seen. Arising from the ruins of the 1906 earthquake and fire, it established San Francisco as the most beautiful city in America."

The Panama-Pacific Exposition was in the planning stages for more than a decade before officially opening on February 20, 1915, so it is unsurprising that there were many historic firsts associated with the fair. Among the most permanent was the five-piece numismatic commemoration by the U.S. Mint. That remembrance would also include a number of firsts, including the first and only fifty dollar coins of the classic commemorative era of U.S. numismatics, from 1903 to 1926.
The fifty dollar octagonal Pan-Pac coins remain today the only octagonal coins ever issued by the U.S. Mint, and both they and their round siblings are hotly contested in any grade at auction. This first-time offering, part of a four-coin set, is sure to appeal to collectors. The piece itself is remarkably well-preserved with pale yellow surfaces touched in more orange. Luster and striking qualities are equally solid, and while a few wispy abrasions are present, the overall eye appeal is great. Just as this coin was the cornerstone of its Panama-Pacific set, it may in turn become the cornerstone of a commemorative collection.