Loon Lake Auxiliary, located in El Dorado County, California, is a rockfill dam primarily used for hydroelectric power generation and recreational purposes. Built in 1963 by Bechtel, this dam stands at a height of 90 feet and has a structural height of 102 feet. It has a storage capacity of 69,309 acre-feet, with a normal storage level of 51,000 acre-feet, covering a surface area of 1,450 acres.

Managed by the Federal Energy Regulatory Commission, the dam is inspected annually and is deemed to have a significant hazard potential. The surrounding area is at high risk, according to a risk assessment, with emergency action plans in place. While the dam has not undergone a recent condition assessment, it is regulated and permitted by the California Department of Water Resources, ensuring its safety and compliance with state standards. Overall, Loon Lake Auxiliary serves as a vital resource for water supply, electricity generation, and recreational activities in the region.