Just under 25 km up from its mouth, the main Gates Valley branches east off the north-aligned Birkenhead River's valley via Poole Creek, which drains the westward side of the Pemberton Pass; Birken Lake at its summit is part of the Gates River system which drains towards Anderson Lake and Lillooet. In this area there is a large stone with a foot-shaped impression on it - still there to this day and witnessed by Alexander Caulfield Anderson on his journey through the area in 1846 - where it is said one of the transformers stamped his foot in the rock to make a boundary between the people of the Canyon and those of the Lillooet River valley, who had converged on the spot bearing salmon (from the canyon) and spatsum (weaving reed-grass, from the Lillooet River). Its location is unmarked and as it is on private land it is not available for viewing.