The Athabasca River, 1231 km long, rises in the Columbia Icefield, flows north through Jasper National Park, then northeast past Fort McMurray, Alta, to Lake Athabasca; it is the southernmost headstream of the Mackenzie River, and its chief tributaries are the Pembina, Lesser Slave and McLeod rivers. In northeast Alberta, it passes through huge deposits of oil sands containing Bitumen. Near the river, the oil sands are close to the surface, and outcrops can be seen on its escarpment. Peter Pond wintered on the river 1778; and the first freight route to the Rockies followed the Athabasca to Jasper and then by pack horses over Athabasca Pass. Goods were later moved by horse north from Edmonton to Athabasca Landing and then by barge along the river. This route fell into disuse when the railway was built from Edmonton to Waterways (1917).