Masonry
Taylor, Michael C. Road of Difficulties: Building the Lower Columbia River Highway
...part of the design for carrying run-off from the road were drains, curbs, and gutters, and the highway represented one of the earliest rural uses of each. Pipe culverts that allowed cross drainage, drop inlets acting as catch basins to direct runoff, and box culverts to cross small creeks and permit cattle to cross under the highway safely were also in the plans. The highway's design even included the use of prototype masonry walls and guard rocks.
Taylor 25-26
The State Highway Department also used a standard arched masonry rail throughout the Columbia River Highway. There were variations to it's design -- most memorably seen near Crown Point and Multnomah Falls on the upper highway -- but they all consisted of slip-form mortared walls of random rubble with arched drainage openings and a concrete cap. Masonry railings were more expensive then other styles, but maintenance costs were very low. The condition of these railings in the abandoned Prescott Point section of the lower highway is still remarkable, given their age and many years of neglect.
Taylor 28
Links
WyEast Blog: Stone Walls of the Columbia River Highway
This article examines Lancaster’s stone walls in more detail. The drawings included in the article are from the Historic American Engineering Record (HAER) program, established in 1969 by the National Park Service to document historic sites and structures.
http://wyeastblog.org/2013/12/15/stone-walls-of-the-columbia-river-highway/