Coolidge Dam
- Vicinity: SW of San Carlos
The Coolidge Dam is a significant structure because it is the first large scale multiple-dome dam ever built and may possibly be the first successful multiple-dome dam of any size ever built. In addition, the Coolidge Dam construction process developed new and unique methodologies and technologies in concrete forming and pouring. Therefore, the Coolidge Dam is a significant structure on two levels: design and construction technology.
The key element of design in the Coolidge Dam is the use of the large egg-shaped domes to form the dam walls and the fact that these massive concrete structures were built with no expansion/contraction joints. The domes are both vertical and horizontal arches which are heavily reinforced with steel to (1) prevent temperature shrinkage cracks (2) anchor the concrete to the foundations and (3) transfer shear forces to the buttresses as the domes approach the crest. The use of reinforcing steel in the domes allowed them to be built as one piece with no joints at all. Moreover, the overall aesthetic appearance of the structure was taken into account. The exterior of the entire dam, including all the concrete surfaces of domes, buttresses, roadway and railings, were finished to a high degree with the application of a special surface compound. This created a smooth finish all over the structure. The architectural features of the dam are also unusual, in that the expenses entailed in building elaborate railings for the roadway, the cornice, the overhangs (complete with eagles), and other ornamental architectural details could have been avoided. However, since the dam was being built as somewhat of a showpiece, these expensive details were added. - NRHP, 14 August 1980