Page:Big Oak Flat Road (HAER No. CA-147) written historical and descriptive data.pdf/16

 hand-laid embankments for the pioneer road were complete, and footings for the cement rubble retaining walls were being excavated. The BPR was supervising 77 men working as day laborers.

Morrison-Knudsen completed the clearing for the Meyer Pass-Crane Flat section in November. Grading work took place the following summer, and by the end of October the road preparation work was complete and accepted. Unlike the Old Big Oak Flat Road and other early Yosemite roads, the new road was rarely built up on fill sections and retaining walls, but rather "cut in" to the cliffs with explosives. Although care was taken to "minimize" the scarring of the Valley cliffs, this marked a departure from the use of local rock features and slopes to carry the road. Some work was done using earlier techniques, such as the building up of major sections on retaining walls, but the roadway design standards were clearly changing.

Surveys for the three new bridges over Cascade, Tamarack and Wildcat creeks were conducted from 1936 to 1938, and the structures were designed in 1937 and 1938; construction began in October of the latter year. Unlike the "rustic style" bridges recently employed in the Valley, the new spans [HAER Nos. CA-83, CA-84 & CA-85] were striking open-spandrel arch bridges, of reinforced concrete poured in place. The bridges ranged from 91' to 106'6" in length. Each had two lanes for traffic and sidewalks, and soared across the creeks on graceful single-span arches. The bridges were completed in October 1939.

The two short tunnels were built in 1936 and 1937. They were constructed by first driving a 6' x 7' foot pilot tunnel, then drilling out the extra dimension. The excavation of 367' long tunnel #1 [HAER No. CA-86] was completed 21 August 1936, and 224' tunnel #2 [HAER No. CA-87] on 14 November. The concrete lining of the two tunnels was not completed until May of the following year. Pouring of the lining for tunnel #1 began in February 1937. By the end of April, the lining was completed, and crews were cutting the arch rings for the east portal. Preparatory work for the lining of tunnel #2 was underway. On the road itself, retaining wall work, sloping and rock cutting continued. Some work on the lower section had to be redone in February 1937 after heavy rains in December had washed out a large section of new fill, blocking the All-Year Highway below with 12' of debris.

B. H. McCain of the Bureau of Public Roads arrived in Yosemite in January 1937 to serve as resident engineer for the construction of the 2,083' tunnel #3 [HAER No. CA-88]. Preparations for boring began in March. Walter Champion, electrical engineer for the Bureau of Public Roads, arrived that month to supervise the construction of a transmission line to power the drilling equipment. The contractor's camp was established in April at Big Meadow, and construction work began in mid-May. Unlike the two smaller tunnels, this structure was bored by the full-face method, with the entire cross-section of the tunnel being drilled and blasted at the same time. All boring was done from the west side. The BPR engineer suggested that this may have been the largest tunnel yet attempted by this method. The actual boring of the tunnel began on 10 June 1937, with 150' driven the first month. At the end of July,