CenturyLink in Rapid City, SD
These numbers are located in the city of Rapid City part of Pennington county. There are a few other subcodes that cover this area as well so take care not to confuse them.
Pennington county is situated in South Dakota and operates MT (UTC -07:00) time. This number group covers the 57701, 57702, 57709, & 57703 zip codes.