Panama-Pacific International Exposition commemorative coins have such an attractive design they are always in demand. The Exposition itself was set up near the Marina in San Francisco, and the colonnade at the Exploratorium still exists today.
The Pan-Pac coins, as they are normally known, were struck in two metals and four denominations. The listed example is the only denomination of the four struck in silver. This example has been graded Mint State 64 by PCGS. A nice original coin!