As a rule it is mountains which offer a deterring barrier to the engineer, but in this instance it was the valleys which presented the most searching difficulties. The practical route for the line lay through the Placer River Valley, and the negotiation of this depression in order to preserve the grade and alignment was beset with innumerable perplexities. After leaving the coast the railway has to climb gradually until it gains and crosses the summit of the watershed at an altitude of 1,050 feet and 45 miles out of Seward. Then comes a sharp drop for 3 miles, followed by a more rapid descent for 200 feet or so. In times gone by a huge glacier filled this valley. At the head the ravine narrows sharply and leads into a canyon, where the rocky wall rises up on either hand almost perpendicularly to a height of some 700 feet. This rift is about three-quarters of a mile in length, and opens into another valley at the foot of a large glacier which leads to a bay on the coast known as Turnagain Arm. So sharp is the descent that in the course of 22 miles some 900 feet has to be overcome. The drop from the summit at the 48th mile-post out of Seward for a distance of 6 miles puzzled the engineers sorely. Six surveys had to be run through this short canyon, and even then a grade of less than double the 1 in 50 was found impracticable. The configuration of the rift did not permit official requirements to be carried out with economy. Even the grade twice that demanded was found unattainable without six tunnels and seven large curves. The survey was a perilous undertaking owing to the extreme steepness of the cliff-sides and the vegetation clinging to the rocky face. The rodmen working with the survey parties had to be slung in mid-air from ropes to enable the requisite calculations to be made. The difficulties of the survey were surpassed by those of construction. The very first tunnel brought this home with startling vividity. It is 700 feet in length, and is almost entirely on a curve of about 400 feet radius burrowing through a projecting hump of the main chain. In order to gain the tunnel a broad sweep of the same radius as that of the tunnel curve had to be made, and the two works together form two-thirds of a circle. But one portal of the tunnel opens out on the brink of a precipice, the mountain-side falling away abruptly at that point. So in order to carry the line forward a huge artificial work had to be carried out. This is a timber trestle which constitutes one of the most outstanding features of the line. From end to end it measures 1,240 feet in length, while it varies in height from 40 to 90 feet, some of the outside members being no less that 120 feet in length. Over 1,000,000 feet of timber was used in its construction.