1915-S Panama Pacific $50 Gold - 1915-S Pan-Pac $50 Octagonal NGC MS64 CAC. This outstanding, near-Gem 1915-S fifty-dollar gold octagonal coin is resplendent with bright mint luster and outstanding surfaces. The grade of MS64 is confirmed by CAC, which indicates that the coin is of premium quality and fully deserves the grade assigned. The surfaces are original, clean, and lovely. A couple of microscopic marks on Minervas cheek probably keep coin from a Gem grade. The strike is full in most areas with full details on Minervas hair and all the peripheral details on both sides. There is slight weakness on Minervas helmet and the owls wing and legs.
Robert I. Aitken designed both the Pan-Pac Round and Octagonal coins, which were two of the five coins to commemorate the Panama-Pacific International Exposition, the opening of the Panama Canal, and the rebirth of San Francisco after the 1906 earthquake and fire. Aitken, a New York artist, also designed the Missouri Centennial half dollar of 1921. In addition he designed the cap of the courthouse in San Francisco. On it is a sculpture of Liberty Enthroned and guarded by Order and Authority. On each side are groups of figure that represent Council and Research modeled after several people involved with the law or creation of the Supreme Court Building.
Farran Zerbe, former President of the American Numismatic Association, oversaw the Expositions official Coin and Medal department and was largely responsible for the distribution of the coins.
The Panama Pacific Exposition was held in San Francisco in 1915. It had great economic importance for the city because of the great earthquake and fire. The expo did much to improve the spirit of the Bay Area and help San Francisco rebound. It ran from February 20th to December 4th, 1915 and was generally considered a huge success. The fair grounds are now the Marina District. The grounds were originally swamp land that was successfully pumped and filled. Piles were driven to support the buildings of the 1915 Exposition. 
The obverse of the coin shows Minerva, the goddess of wisdom, skill, contemplation, spinning, weaving, agriculture, and horticulture. From the 2nd century BC onwards she is equated with the Greek goddess Athena. Like Athena, Minerva was born from the head of Zeus or Jupiter (the Roman god). In Rome Minerva took on the warlike character that she shared with Athena. She is often depicted with an owl, as on this coin. The owl is her sacred creature and, because of this connection, a symbol of wisdom. It is also a symbol of status, intelligence, and wealth.
On the coins obverse, Minerva is facing left wearing a stylized helmet. Above her head is the motto IN GOD WE TRUST. The legend UNITED STATES OF AMERICA and FIFTY DOLLARS all separated by dots are around the periphery. The date, on an arc or banner, is written in Roman numerals MCMXV, following the precedent of Augustus Saint-Gaudens double eagles. The reverse shows the owl, perched on a branch of pine. Behind the owl is the motto E PLURIBUS UNUM. The legend PAMAMA-PACIFIC EXPOSITION SAN FRANCISCO encircles the reverse. The S mintmark is in the field between the inner border and the rightmost cone.  A pattern of beads and reels separate the legends of both sides from the main elements of the design. The octagonal coin has the same design as the round piece, but it also has dolphins in the eight angled exergues on both sides. The coin has a weight of 1,290 grains which is equal to 83.59 grams. It is 44 millimeters in diameter, is composed of 90% gold, and has a reeded edge.
The original design of the coin showed a spider web, as a symbol of industry. However, this element was criticized by the Secretary of Treasury, William Gibbs McAdoo, and Aitken removed it before Engraver Charles Barber redid the design. Cornelius Vermeule, writing in Numismatic Art in America found the coins design to be laudable. He said, There were a minimum of inscriptions, classic Greco-Egyptian profile of Athena in full panoply, the date in Roman numerals, and a naturalistic owl in a mass of western pine cones.In an overall view, the arresting feature of the giant gold coin was its archaistic treatment of details and relief.[The coin is] a tour de force, dated to be sure, but unusual enough in all respects to be worthy of what American numismatic art could achieve when creativity and Mint technique worked in unison.
The first striking was on June 15, 1915. Originally 1,500 coins were struck, but 864 were melted for bullion leaving a net mintage of just 645 pieces. This amount is the second lowest distribution figure for any United States commemorative coin. Only the round fifty dollar Pan-Pac had a lower net mintage.
The coins were sold individually and in sets. A single set showed one of each Panama-Pacific coin: the silver half dollar, the gold dollar, the quarter eagle, the fifty dollar round and the fifty dollar octagonal. They were also offered as a double set showing both the obverse and reverse designs. These sets were placed in velvet covered trays that were mounted under glass in a hammered metal frame and accompanied by the artists interpretation of the designs. They were also sold in a velvet-lined leather case and in boxed sets of the three lower denominations and the buyers choice of the fifty dollar round or octagonal coin.  The octagonal pieces proved more popular at the time perhaps because it was a reminder of the Gold Rush days. Numismatists of the time liked the Panama-Pacific coins. At least a hundred sets were sold to them. But most of the 300 sets went to the wealthy citizens of San Francisco, bankers, convention officials, and members of the general public.
The official sale price was one hundred dollars, which included one each of the fifty-cent, dollar, two-dollar and fifty cent, and fifty dollar coin. A full set, with both fifty-dollar coins, cost two hundred dollars, and a double set was available for four hundred dollars. Five years after the termination of the original sales, the set of five coins was valued between three and four hundred dollars.
Because of its low net mintage, all Pan-Pacific fifty dollar coins are rare and eagerly sought after by collectors and specialists. For many collectors the fifty dollar octagonal is a trophy coin because of its lovely design, unusual qualities and low net mintage of just 645 pieces. Bowers writes in his A Guide Book of United States Commemorative Coins: "Each of the five Panama-Pacific International Exposition coins is in strong demand today. Most activity is necessarily centered around the varieties with the largest distribution -- the half dollar in particular, but also the gold dollar. Quarter eagles are scarce. The $50 issues play to a wide market as 'trophy coins,' often sought by well-financed buyers who otherwise are not particularly interested in commemoratives. There was a time when cased sets, particularly those in copper frames, were the crme de la crme of the commemorative specialty. In recent years most such sets have been disassembled since most owners prefer to have the five coins in individual certified holders marked with their grades." In its population report, as of August 2012, CAC shows 28 in MS64 condition with 6 better.