Ryan, KEØLXT, has set up an EchoLink node that he has opened for general use. It's on 147.420 MHz and the node number is 489225.
Northern Hills Linked Repeater System
The Northern Hill Amateur Radio Club maintains a system of three linked VHF repeaters that provide coverage to northeastern Wyoming, western South Dakota, and northwestern Nebraska. All use the standard repeater offsets.
Hot Springs Club Repeaters
The Hot Springs Amateur Radio Club maintains four repeaters in the southern and central Black Hills.
South Dakota Link Repeaters
The amateurs in South Dakota maintain a network of statewide linked repeaters.
Here is a map of the system.