The Mountain Dell Dam provides a water equalizing and storage reservoir for Salt Lake City, Utah located east of the city in northeastern Salt Lake County, near Interstate 80 in Parley's Canyon. Designed by John S. Eastwood, and constructed between 1914 and 1925, the dam is an example of a mixed buttress dam and multiple arch dam construction. At the time the plans were made, the city was in need of a sufficient supply of water, especially during late summer and the middle of winter. With the completion of the dam, the city had an available storage capacity of , and distributing or equalizing capacity of compared to previously. The dam was listed on the National Register of Historic Places in 1980. Mountain Dell Dam is listed as in "poor" condition and is under repair. Design Plans were made for three types of dam: Arched solid dam, gravity type Reinforced concrete dam of the Ambursen type Multiple arch reinforced concrete dam of the Eastwood design After consideration, the multiple arch type was chosen. One of the factors influencing this decision was the bedrock condition at the site. The bedrock is a calcareous shale not entirely watertight and of a nature to decompose somewhat under exposure to air and water. The advantages of the multiple arch type in this connection were considered to be the practical elimination of upward pressure, the practical impossibility of overturning or sliding on its base and the ready facilities for internal inspection of the dam at any time. Construction The dam was built in two stages, the first stage completed in 1917 with a height of above the foundation and the second stage, completed 1925, added to the height of the dam. The cost of the structure was considerably increased because of the necessity of going below ground level in the bottom of the canyon to secure the bedrock foundation. The spillway level is below the top of the dam, so that the maximum depth of the reservoir is to the crest of the spillway. The dam as planned and as constructed consists of 11 buttresses and 11 arches in the first stage and an additional 5 buttresses and 5 arches in the second stage. The maximum base width of the dam is from the face of the arch to the downstream end of the buttresses. The maximum thickness of the buttresses is . The maximum