Path 66 consists of the northernmost segment of TANC's 500 kV line from Captain Jack substation to Tracy substation in California's Central Valley. Leaving Captain Jack substation, the line first heads southeast as a single-circuit line and runs parallel with the other two 500 kV lines across the Modoc Plateau. It then turns west and climbs in elevation and reaches its highest point near Grizzly Peak at about . From there, it heads south, spanning over the Stonecoal Valley and the Pit River. Near Round Mountain, it turns southwest and the line is joined by two 230-kV lines as all three lines head into the Sacramento Valley. As the line passes by Cottonwood, it turns west and crosses Interstate 5. Near Olinda, it turns south and enters Olinda substation. Here the line interconnects with transmission lines carrying power from Shasta Dam and Keswick Dam.