| Boulder to Caguas (Puerto Rico) | 2,771.79 mi (4,460.76 km) |
| Boulder to Cahokia (Illinois) | 811.27 mi (1,305.61 km) |
| Boulder to Calabasas (California) | 842.71 mi (1,356.21 km) |
| Boulder to Caldwell (Idaho) | 637.58 mi (1,026.09 km) |
| Boulder to Caledonia (Wisconsin) | 918.81 mi (1,478.67 km) |
| Boulder to Calera (Alabama) | 1,129.23 mi (1,817.33 km) |
| Boulder to Calexico (California) | 761.92 mi (1,226.19 km) |
| Boulder to Calhoun (Georgia) | 1,177.56 mi (1,895.10 km) |
| Boulder to California (Maryland) | 1,538.56 mi (2,476.07 km) |
| Boulder to California City (California) | 767.41 mi (1,235.03 km) |
| Boulder to Callaway (Florida) | 1,302.08 mi (2,095.50 km) |
| Boulder to Calumet City (Illinois) | 930.42 mi (1,497.37 km) |
| Boulder to Calverton (Maryland) | 1,503.22 mi (2,419.19 km) |
| Boulder to Camano (Washington) | 1,019.99 mi (1,641.51 km) |
| Boulder to Camarillo (California) | 857.10 mi (1,379.36 km) |
