| Difficult Run to Fortuna Foothills (Arizona) | 2,106.00 mi (3,389.28 km) |
| Difficult Run to Foster City (California) | 2,414.89 mi (3,886.39 km) |
| Difficult Run to Fostoria (Ohio) | 356.68 mi (574.03 km) |
| Difficult Run to Fountain (Colorado) | 1,466.57 mi (2,360.22 km) |
| Difficult Run to Fountain Hills (Arizona) | 1,938.98 mi (3,120.49 km) |
| Difficult Run to Fountain Inn (South Carolina) | 395.37 mi (636.29 km) |
| Difficult Run to Fountain Valley (California) | 2,270.20 mi (3,653.54 km) |
| Difficult Run to Fountainebleau (Florida) | 923.72 mi (1,486.59 km) |
| Difficult Run to Four Corners (Oregon) | 2,350.74 mi (3,783.15 km) |
| Difficult Run to Four Corners (Texas) | 1,221.08 mi (1,965.14 km) |
| Difficult Run to Four Square Mile (Colorado) | 1,467.91 mi (2,362.38 km) |
| Difficult Run to Fox Crossing (Wisconsin) | 681.87 mi (1,097.37 km) |
| Difficult Run to Fox Lake (Illinois) | 617.34 mi (993.52 km) |
| Difficult Run to Framingham (Massachusetts) | 389.11 mi (626.21 km) |
| Difficult Run to Franconia (Virginia) | 13.70 mi (22.05 km) |
