Location: SD-79 and SD-40, Hermosa Immediately after the 40 east turn, we’ll approach 40 west. Stay on SD-79 to head to US-18 (erroneously signed as SD-18). Follow 40 west to Keystone and Mt. Rushmore. Location: SD-79 and SD-40, Hermosa Turn right for 40 west. Stay straight for 79 south.  S to SD-36, N to US-16 … Continue reading South Dakota Highway 79, SD-40 to SD-40