Three Forks, United States offers 1 beach perfect for sunbathing, surfing, swimming, and more. Three Forks, South Dakota, United States, is known for the Lewis and Clark Expedition historical sites. The best time to travel to Three Forks, United States, is in late spring or early fall when the average air temperature is around 60-70°F, and the water temperature in nearby rivers is approximately 50-60°F. Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!