Page:Big Oak Flat Road (HAER No. CA-147) written historical and descriptive data.pdf/17

 the bore had reached 347'; excavated material was being stockpiled to be ground for surfacing. In August, the tunnel advanced to 620', but the following month witnessed delays as soft rock was encountered, requiring timbering and guniting for safety measures. A 180' adit was to be driven to the cliff face to provide for ventilation. Construction of the long tunnel employed a drilling "jumbo," a device built specifically for use on the project. The large machine, mounted on a 5-ton Liberty truck, had six separate drills that were used to bore holes for the blasting.

Considerable progress was made at the same time on the construction of the road itself, but not without human cost; Ernest Messien, a construction, worker fell on the job and died a little later from complications. By this point, the stone retaining walls from Wildcat Creek to the Valley were complete, and stone was being cut for the guard walls which would border the road. Sample sections of the guard wall were built in November.

Work crews on the long tunnel passed the soft rock area in October 1937 and began to make much better progress. The half-way point was passed in November. Severe rainstorms filled the lower end of the tunnel up with 10' of water in December, and operations were hampered again; nevertheless, by the end of the year, the bore was in 1,160'. In January 1938, the tunnel bore reached 1,420', and drilling began on the ventilation adit, which was completed in February. The long tunnel was holed through on 22 April 1938, and the final work, including the laying of curbs and drains and preparation of the road surface was completed on 10 September.

A large part of the road between Meyer Pass and the Valley floor was built on fill or benchwork, requiring heavy stone retaining walls. These walls were constructed of irregularly sized granite stone, placed by hand-operated mast-and-boom derricks; these derricks were moved ahead by mule train. Cut stone blocks were also placed on the arch rings of the two lower tunnels. This stone was taken from a large boulder on the Coulterville Road by the contractor, the Union Granite Company of Rocklin, California. The final construction report gives some details of their construction:

"Full size wooden templates were built for the required arch ring stones before cutting stone for the tunnels was started...in general the stones were blasted into slabs and cut, with plugs and feathers, roughly to the desired size. Contact faces were then trued up and smoothed on a finishing machine constructed on the job. A hand derrick, mounted on top of the concrete lining just back of the portal, was used to hoist and set the ring stones and the rocks used in the portal wall."

Original plans called for the walls to be constructed of smooth-faced quarried stone blocks. However, the finished work did not successfully blend with the rugged terrain, and following consultations with the National Park Service landscape architecture division, the BPR decided to construct the faces of the walls from rougher, irregularly-sized stones.