lubbock
Kirk, Colorado is halfway between Amarillo & Rapid City
Amarillo, TX
Knob Hill, TX.
Temple, TX
Amarillo Tx is 8 hours from either location
A rough estimate would be Amarillo, Texas.
Vernon, Tx is as close to halfway as far as a town that has restaurants and gas and stuff.
Hewitt, Texas
Interstate 35, Guthrie, OK 73044.
White River City, Colorado is the halfway point.
The halfway point is Clarendon, TX. I would stay in Amarillo.
Crockett Heights, Texas