The G Line's northern terminus was at Nine Mile Station in Aurora on the I-225 branch of the system, while its southern terminus was at Lincoln Avenue Station in Lone Tree. The G Line was one of very few tangential ("suburb to suburb") rail transit lines in the United States.
According to a map in the RTD's service plan for the corridor, the G Line's color was brown. In August 2007, night, Saturday, Sunday and holiday service on this route was discontinued due to low ridership. An exception was the lone northbound Owl service trip on weekend and holiday mornings. The owl train traversed both the E & H Lines by way of the G Line link. Service was further reduced to peak hour-only in August 2008 before being eliminated entirely on May 3, 2009.