The author begins the story calling Tin Cup a ghost town because it a) demonstrates what the discovery of gold can lead to.
This choice emphasizes the transformation of Tin Cup from a bustling town during gold and silver strikes to a place that now features only a few summer homes, reflecting the boom-and-bust cycle typically associated with mining towns. The focus on its current status as a ghost town underscores the lasting impact that the discovery of gold has on towns and their populations.