At Ashcroft, the Thompson Canyon begins and the river turns southwestward to its confluence with the Fraser. The river is paralleled by the Trans-Canada Highway, the Canadian Pacific Railway and the Canadian National Railway. From Ashcroft to Lytton, the river is completely confined within Thompson Canyon, making for spectacular scenery. The Thompson River joins the Fraser River in Lytton. There is a striking stretch of dark black cliffside just downstream from Ashcroft and visible from the Logan Lake-Ashcroft highway is officially named the Black Canyon. Just below the town of Spences Bridge was the site of a major rail disaster in the early 20th century. Communities along this section are Bighorn, Shaw Springs, and Goldpan. Geology The Thompson River valley has existed in some form for at least 50 million years; however, for much of its history, it did not drain to the southwest into the Pacific Ocean as it does today. Geologists believe water from the river flowed northward, through the Cariboo region, eventually entering what is the modern-day Peace River drainage basin and ending up in the Arctic Ocean. This flow direction is estimated to have ended approximately 2 million years ago, as the Pleistocene era of heavy glaciation began. Glacial lakes During the era of massive glaciers in the Thompson River valley, water from the area likely drained eastward, through the Shuswap Lake area into what is now the Columbia River drainage. This flow direction was influenced by large ice buildups in the Thompson valley, which created extensive glacial lakes. Two large glacial lakes, Glacial Lake Thompson and Glacial Lake Deadman, occupied much of the modern river's course from 13,000 BCE to 10,000 BCE. These deep, narrow, ribbon-shaped lakes held large volumes of water; Glacial Lake Thompson held nearly at its highest point. The lake stretched from Spences Bridge in the west to the eastern reaches of Shuswap Lake, as well as far up the northern reaches of the North Thompson river valley. The last large glacial lake, Lake Deadman, was drained by a catastrophic ice dam failure, called a jökulhlaup, in about 10,000 BCE. This event released as much as of water southwest into the Fraser River system, possibly depositing sediments as far away as the Salish Sea, more than away. From this point, the Thompson waters stopped flowing eastward into the Columbia River system, and the river became a tributary of the Fraser. Landslides Because