Alpine Auxiliary No. 4, located in Dorrington, California, is a rockfill dam primarily used for hydroelectric purposes, with additional benefits for recreation and water supply. Managed by a private entity, this dam stands at a height of 12 feet and has a storage capacity of 4,300 acre-feet, serving the surrounding area with a normal storage level of 4,120 acre-feet. The dam is situated on Silver Creek and falls under the jurisdiction of the Department of Water Resources (DWR) for safety regulations and inspections.

Operated under the oversight of the Federal Energy Regulatory Commission (FERC), Alpine Auxiliary No. 4 has a spillway width of 99 feet to handle a maximum discharge of 1,850 cubic feet per second. Despite its low hazard potential, the dam is subject to regular inspections with an inspection frequency of 1 year. The emergency action plan (EAP) for the dam was last revised in December 2020, ensuring that necessary measures are in place to mitigate risks and protect downstream communities in case of emergencies.

With a moderate risk rating of 3, Alpine Auxiliary No. 4 is a vital component of the local water infrastructure, contributing to the region's energy production and water management needs. As enthusiasts for water resources and climate, understanding the design, purpose, and regulatory framework of dams like Alpine Auxiliary No. 4 is crucial for ensuring the safety and sustainability of water sources in California's Alpine County.