The journey up the Finlay River's 450 km length and up its tributaries, the Toodoggone River and the Firesteel River, took Black and his men to what is considered the ultimate source of the Mackenzie River at Thutade Lake (at the head of the Firesteel). Proceeding sometimes on foot, sometimes by raft, Black and a smaller crew explored the region of the Spatsizi Plateau, there finding one of the sources of the Stikine River and so reaching the boundary between the Arctic and Pacific drainages. Journeying north-eastward, Black crossed another divide — this time between the Stikine and Liard Rivers — and rafted some way down the Kechika by way of its tributary, the Turnagain River, before returning again down the Finlay.