In 1870 the task of laying some 2,500 miles of track was commenced. The mouth of the Columbia River was selected as the outlet on the Pacific Ocean. Work was commenced simultaneously from both ends, the eastern terminal being near Lake Superior. By 1873 the line had reached the Missouri River on the east, and here a pause had to be called to erect a massive steel bridge, 1,400 feet long, 50 feet above the river, which absorbed £200,000, or $1,000,000. When the first stretch of prairie line was completed, it was used only in the summer months. There was not enough traffic to pay for the coal burned in the locomotives during the winter, in the estimation of the administration, while they feared the expense and losses that would be inflicted by the terrible blizzards and snowstorms which rage in this country. Consequently, after the crops had been garnered and conveyed to market, all the engines, trucks and cars were withdrawn from service upon a great length of line, which was abandoned practically until spring came round. This state of affairs continued until the Indians rose up against American law and order, wiped out several men, and precipitated a general reign of terror. The Government, in order to pour troops into the disaffected territory, requested the working of the railway during the winter of 1876–7, which proved to be one of the most severe in history. Yet the line suffered less from snow than the systems in the eastern States, and, moreover, possibilities of traffic were discovered which hitherto had been considered non-existent. Needless to say, the railway never has been closed during the winter since. Before the railway had proceeded half-way across the continent, the need for overhauling and relaying the first part of the track was felt. A higher standard of construction was therefore laid down for all the new work. Moreover, in order that the line should be completed within the shortest time possible, it was split into large sections, and the grade was driven east and west from several points simultaneously. [Illustration: THE “SWITCHBACK” BY MEANS OF WHICH THE GREAT NORTHERN RAILWAY OF THE UNITED STATES NEGOTIATED THE CASCADE MOUNTAINS BEFORE THE BORING OF THE CASCADE TUNNEL] The mountains proved a severe stumbling-block and precipitated great delay. The country was so broken that lofty timber trestles had to be erected to be filled in with earth at a later date. Then two large tunnels had to be bored to carry the track through the Rockies, one, the Bozeman tunnel, being 3,610 feet long, and the other, the Mullan tunnel, 3,857 feet from end to end. Yet construction proceeded so successfully that the links were joined up on September 3, 1883, the last spike being driven in Hellgate Canyon, Montana. The spike used for this auspicious event was the very first that had been driven in connection with the line when it was commenced years before. [Illustration: BUILDING A STEEL TRESTLE ACROSS A RIFT