| Difficult Run to Smyrna (Delaware) | 97.09 mi (156.25 km) |
| Difficult Run to Smyrna (Georgia) | 529.05 mi (851.43 km) |
| Difficult Run to Smyrna (Tennessee) | 542.52 mi (873.10 km) |
| Difficult Run to Snellville (Georgia) | 508.29 mi (818.01 km) |
| Difficult Run to Snoqualmie (Washington) | 2,284.63 mi (3,676.75 km) |
| Difficult Run to Snyder (Texas) | 1,383.28 mi (2,226.17 km) |
| Difficult Run to Socastee (South Carolina) | 371.96 mi (598.61 km) |
| Difficult Run to Socorro (Texas) | 1,698.23 mi (2,733.03 km) |
| Difficult Run to Soddy-Daisy (Tennessee) | 499.27 mi (803.49 km) |
| Difficult Run to Solana Beach (California) | 2,251.07 mi (3,622.75 km) |
| Difficult Run to Soledad (California) | 2,388.73 mi (3,844.28 km) |
| Difficult Run to Solon (Ohio) | 276.00 mi (444.18 km) |
| Difficult Run to Somers Point (New Jersey) | 149.69 mi (240.91 km) |
| Difficult Run to Somerset (Kentucky) | 414.86 mi (667.65 km) |
| Difficult Run to Somerset (New Jersey) | 187.63 mi (301.96 km) |
