The route laid not only had to go across rivers and canyons, which had to be bridged, but also through two mountain ranges—the Sierra Nevada and the Rocky Mountains—where tunnels had to be created. The explosions had caused many of the Chinese laborers to lose their lives. Due to the wide expanse of the work, the construction had to be carried out at times in the extreme heat and also in other times in the bitter winter cold. So harsh were the conditions that sometimes even entire camps were buried under avalanches.