Gradients. Some reference has been made in the previous chapter to the elevations which the Central Pacific had to surmount. The highest point which the company had to reach was Summit Station, 105 miles from Sacramento, at an altitude of 7,042 feet. Since Sacramento lay only 56 feet above sea level, to reach this point required an ascent of 6,986 feet in a distance of 105 miles, more or less, according as the route chosen was longer or shorter. The company’s engineer said in 1864 that if it had been possible to maintain a continuous ascending grade, the maximum grade, from the foothills to the summit of the Sierras could have been reduced to 80 feet per mile.
In the attempt to approach this ideal condition the Central Pacific surveyed and resurveyed continuously until its rails were actually on the ground. Barometrical reconnaissances were made in 1862 and 1863 on lines via Downieville and Yuba Gap, and via Oroville and Beckwourth’s Pass, in addition to the surveys via Georgetown, Dutch Flat, and Henness Pass, to which earlier reference has been made (page 20).[95] Location surveys reached Alta in 1863, the state line in 1866, and Ogden in 1868.[96] After Mr. Judah’s death almost an entire relocation of the line from the 31st to the 48th section was made in 1864 in order to avoid tunneling, and to reduce cost,[97] and still later it was found desirable to shift the whole route between Dutch Flat and Emigrant Gap from the Bear River side of the ridge, up which the Central Pacific was proceeding, to the American River side. This change avoided some 20 miles of 116-foot grade, together with a great deal of curvature.[98]
The final result of these various surveys was a line with maximum grades of 116 feet to the mile. This does not compare unfavorably with most of the transcontinental routes subsequently built. It is interesting to observe, however, that the Central Pacific summit is some 2,000 feet higher than the altitude of Beckwourth’s Pass, and that the maximum grade of the Western Pacific Railway, built years afterwards through that pass, is only 52.8 feet to the mile, or one per cent. Neither Judah nor his immediate successors, therefore, discovered the best route across the Central Sierras.
Temperature. A second physical difficulty incident to mountain construction was found in the mountain climate. The summer climate of the Sierras is delightful, at least at altitudes of about 6,000 to 7,000 feet. At lower elevations the temperature is often uncomfortably warm. But the winter climate is quite different. As early as August the nights begin to get cold, the first snows come in November, while in January the trails become impassable, and the high levels are unvisited by man until the following year. The official record shows that the greater part of the mountain construction on the Central Pacific occurred between July, 1866, and July, 1868.
Mr. Stanford has testified that both the winter of 1866-67 and that of 1867-68 were unusually severe, and his engineers have dwelt in great detail upon the consequent impediments to their work. Not only did the frozen earth resist pick and shovel, but there were snow banks from 30 to 100 feet deep. It was necessary to remove this snow to permit excavation, and to keep clear the space to be occupied by embankments in order to prevent settling. When the summit was approached tunnels had to be driven through the snow to the rock face. As the whole working force could not be employed in the tunnels, the surplus labor, with all its supplies, was hauled beyond the summit and put to work, at great expense, in the cañons of the Truckee River. The first snow sheds were built in the summer of 1867, and in the following years it was decided to cover all the cuts and points where the road crossed the paths of the great avalanches beyond the summit. The total length of sheds and galleries built by the fall of 1869 was 37 miles, and the cost was $2,000,000.[99]
In addition to the difficulties caused by snow, it must be remembered that the frozen earth, though uncovered, was difficult to work. Not only was it necessary to blast out material which could have been cheaply moved at a more favorable time, but, when piled into embankments, the ground settled in the spring as the frost was leaving, and required constant attention.[100]