This Gaviota Gorge Tunnel (51 0172R) is a reinforced-concrete tunnel measuring approximately 420 feet long, 35 feet wide, and 22 feet tall. The raised curb on the west side is approximately 2 1/2 feet wide, while the east side has a 4-foot-wide walkway. The interior of the tunnel is smooth concrete with two rows of mounted square light fixtures. At the portal entrances the concrete is incised with lines that imitate coursed masonry and give the portals a rusticated, Romanesque appearance. The concrete is tinted to match the natural Gaviota sandstone. The portal openings are bordered by arched forms with a slightly protruding lip and inward-sloping faces. They are scored to give the appearance of masonry arches, with prominent keystones. Both portals have a "1953" date stamp at the base of the arch on the right side. The south portal has wide pilasters on both sides. Weep holes with projecting, trapezoidal drain blocks are located near the top of each pilaster. The north portal has a side wall with an ornamental, round opening. In other areas, the original color of the concrete has been darkened somewhat by vehicle exhaust.