works had started production in 1864 after the U.S. Civil War had cut off shipments of black powder from the East to the mining and railroad industry of California and Nevada. The Central Pacific was a prolific user of black powder, often using up to 500 kegs of each per day. The summit tunnel (Number 6), , was started in late 1865, well ahead of the railhead. Through solid granite, the summit tunnel progressed at a rate of only about per day per face as it was being worked by three eight-hour shifts of workers, hand drilling holes with a rock drill and hammer, filling them with black powder and trying to blast the granite loose. One crew worked drilling holes on the faces and another crew collected and removed the loosened rock after each explosion. The workers were pulled off the summit tunnel and the track grading east of Donner Pass in the winter of 1865–66 as there was no way to supply them, nor quarters they could have lived in. The crews were transferred to work on bridges and track grading on the Truckee River canyon. In 1866 they put in a vertical shaft in the center of the summit tunnel and started work towards the east and west tunnel faces, giving four working faces on the summit tunnel to speed up progress. A steam engine off an old locomotive was brought up with much effort over the wagon road and used as a winch driver to help remove loosened rock from the vertical shaft and two working faces. By the winter of 1866–67, work had progressed sufficiently and a camp had been built for workers on the summit tunnel which allowed work to continue. The cross section of a tunnel face was a , oval with an vertical wall. Progress on the tunnel sped up to over per day per face when they started using the newly invented nitroglycerin—manufactured near the tunnel. They used nitroglycerin to deepen the summit tunnel to the required height after the four tunnel faces met, and made even faster progress. Nearly all other tunnels were worked on both tunnel faces and met in the middle. Depending on the material the tunnels penetrated, they were left unlined or lined with brick, rock walls or timber and post. Some tunnels were designed to bend in the middle to align with the track bed curvature.