 It is believed that a sub-population of Lahontan cutthroats became isolated in Silver King Creek above Silver King Canyon Gorge after erosion made the gorge impassable to trout swimming upstream, probably between 5,000 and 8,000 years ago.The upstream population then adapted to local conditions independent of the larger population below that had evolved in pluvial Lake Lahontan during the Pleistocene.Although Lahontan cutthroats are heavily spotted, the isolated sub-population lost virtually all spotting, perhaps because spots made fish more visible and susceptible to predation in the ultra-clear and shallow mountain stream.