During the summer of 1866, Collis saw Delphine only once, and then she ignored him. A week later he heard that she had left Sacramento and had gone to San Francisco to work in a parlour house on Dupont Street. He often heard about her after that, from Maria-Mamuska in particular, but he never saw her again, ever.

By the winter of 1866, the Chinese railroad gangs had started work on the last and the longest of the six tunnels which took the Sierra Pacific up to the very summit of the mountains. Once they were over the top, there were still nine more tunnels to be bored before the railroad could reach the flatlands of Nevada, and Charles had already assigned digging to be started on these tunnels, night and day. But the Summit Tunnel was what he always called ‘the pig’, and both he and Collis took personal charge of the excavations.

To complete the Summit Tunnel, they had to bore a hole 20 feet high through 1659 feet of totally solid granite, over 7000 feet above sea level. It would have been a pig in the summer, but in the harsh winter of 1866—7, it was a struggle that drove Collis to the limits of his physical and emotional endurance. There were over forty blizzards that winter, and drifts so deep that the Chinese had to tunnel their way through the snow just to reach the face of the rock.

Three times during January, Charles asked Collis to let up; to wait until the thaw. But each time Collis refused. If he could stay up in the High Sierras in the bitter cold, then so could the Chinese, and so could Charles, for that matter. Every day Collis would visit each tunnel heading — the crew that was gradually blasting its way uphill and the crew that was equally gradually blasting its way downhill. Every day he watched drill bits breaking on the impossibly hard granite, as the workers sweated to bore holes that were deep enough to take an effective charge. Every day he restlessly paced his timber hut by the western heading of the tunnel, with his maps and his charts spread out on the table, and the windows blind with snow.

In March, Leland made the journey up to Summit Tunnel and brought with him a large smoked ham, a pound of good Virginia tobacco, and a bottle of nitroglycerin. Nitroglycerin had recently been invented in Europe, he had heard, and was an admirable explosive. In fact, European engineers called it ‘blasting oil’. Collis ignored the ham and the tobacco and immediately called on his Chinese powder monkeys to make some tests with the explosive. For the next three weeks, to Collis’s increasing excitement, the Chinese blew out foot after foot of granite with the new oil, and by 15 April, Charles was predicting that they could be through the mountain by the end of July.