Union Auxiliary No. 2, located in Dorrington, California, is a privately owned rockfill dam with a primary purpose of hydroelectric power generation. This dam is regulated by the California Department of Water Resources and is also inspected and enforced by federal agencies like the Federal Energy Regulatory Commission. With a height of 7 feet and a hydraulic height of 6 feet, Union Auxiliary No. 2 has a storage capacity of 3,283 acre-feet and serves multiple purposes including recreation and water supply for the surrounding area.

Situated on the North Fork Stanislaus River, Union Auxiliary No. 2 has a spillway width of 40 feet and a surface area of 215 acres. The dam has a low hazard potential and a moderate risk assessment rating. Although the condition assessment is not available, the Emergency Action Plan was last revised in December 2020, indicating the dam's readiness for any potential emergencies. Despite its relatively small size, Union Auxiliary No. 2 plays a significant role in water resource management and climate resilience in the Alpine County, California region.