Mountain Dell Dam, Arch dam in Salt Lake County, United States.

Mountain Dell Dam is an arch dam made of concrete in Salt Lake County that holds back water for the region's supply. The curved structure distributes water pressure evenly across its surface, making it an effective water storage system.

Designed by John S. Eastwood, the dam was built in two stages: the first 105-foot section was completed in 1917, and a 40-foot addition followed in 1925. It was listed on the National Register of Historic Places in 1980. In 1983, snowmelt flooding nearly overtopped the structure, prompting the construction of Little Dell Dam upstream and a reduction of Mountain Dell's storage level.

The dam was listed on the National Register of Historic Places in 1980. Its design by John S. Eastwood, a specialist in multiple-arch dams, is a key reason for that recognition. The structure remains a landmark of early 20th-century water engineering in Utah.

The dam is accessible via paved roads, making it easy to reach by car. The surrounding area offers good opportunities for outdoor activities like hiking and fishing near the water.

The dam's multiple-arch design was chosen partly because the calcareous shale bedrock is not watertight and decomposes when exposed to air and water; the arches eliminate upward pressure and allow internal inspection. The structure contains 8,271 cubic yards of concrete and cost $90,000.