1915-S Panama-Pacific Exposition $50. Octagonal. MS-65 (PCGS). Gorgeous medium gold surfaces are fully lustrous with a delightful satin to softly frosted texture. Expertly produced with sharply rendered design elements, both sides are equally well produced and far superior to what is typically offered for this scarce and conditionally challenging classic commemorative type.In San Francisco, a one square mile section of the Marina District was selected and elaborate exhibit buildings were built using impermanent materials. Only one structure, the Palace of Fine Arts, still stands in its original location (two other structures were dismantled and erected elsewhere). Exhibits were set up from around the world that were seen by nearly 19 million visitors over the course of the exposition. Souvenirs were aplenty, including the five commemorative coins, medals, photographs, books, postcards, and even silent movies. One portion of the exposition highlighted the California Gold Rush and sold gilt brass medals in imitation of the famous United States Assay Office of Gold $50 slugs. The two $50 gold coins were inspired by similar coins, also called slugs, that were issued during the Gold Rush. The initial Congressional authorization called for 1,500 examples of each format to be struck, along with several additional pieces reserved for assay purposes.Designed by noted San Francisco sculptor Robert Ingersoll Aitken, the motifs were selected to emphasize the triumph and economic power of California. The obverse on both types bears a bust of Athena wearing a Corinthian helmet and with part of a round shield at her shoulder inscribed with the date of issue, MCMXV. Aitken selected Athena to represent skill, agriculture, horticulture, cultivation, spinning/weaving, and wisdom. The reverse bears a representation of Athenas owl perched upon a branch from what is likely a Coulter Pine (<em>Pinus coulteri)</em>, a tree found along Californias coast and known for its huge pine cones. On the octagonal pieces, swimming dolphins were placed surrounding the central design. The mintmark S appears to the right of the pine cone on the owls right side. The Panama-Pacific commemorative coins hold the distinction of being not only the first commemorative coin struck at a branch mint, but also the first to employ the motto, In God We Trust.In the end, 645 of the Octagonal $50 gold pieces sold and the rest were sent back to the Mint to be melted. While they did not circulate, the octagonal pieces were particularly prone to mishandling due to their size and the softness of the metal which meant they could be easily dinged and scratched. Today, the few extant examples, while generally Mint State, are mostly at the Choice level. Here is an outstanding Gem specimen of this unique commemorative design that celebrates one of the engineering marvels of the world as well as the heroic resurrection of a great Pacific Coast city. From the D. Brent Pogue Collection.