Original dotted lines on this ca. 1938 photo of the south portal show where the Newhall Auto Tunnel and the mountain above it are to be blasted away.
As the age of the automobile descended on the Newhall Pass, Beale's Cut proved to be too difficult a climb for
this new mode of transportation. Therefore in 1910, the 435-foot-long Newhall Auto Tunnel was constructed a quarter-mile to the
northwest of Beale's Cut. Just 17½ feet in width, the tunnel was quite narrow, making it difficult for two-way traffic to pass through.
By 1938, with increasing
auto and truck traffic, the California Division of Highways determined it needed to be replaced. In July of that year, the mountain above the tunnel was blasted
away, and a four-lane road was built above the level of the old tunnel. It was first known as Highway 6, then Highway 14, and
finally as the present-day Sierra Highway. The cutout of the mountain where the tunnel was located can still be seen
today on Sierra Highway at the crest of the Newhall Pass.