Yes, there was a real gold mine in Washington DC
There really was a working gold mine inside the District. The Rock Creek workings were prospected after the Civil War, when a soldier who had panned in California recognised the quartz, and a shaft was sunk near what is now the Gold Mine Loop trail. It never paid. The District sits on the eastern edge of the same Appalachian gold belt that runs down through the Carolinas, so the colour was real even if the fortune was not.
Rock Creek Park, northwest Washington
See it on the map
Commons photos · Atlas Obscura · US National Register · Mindat · Britannica · USGS place names · GeoNames · OpenStreetMap
Other places on the map within a couple of hours.
