Union Main, also known as Union No. 1, is a privately owned dam located in Alpine County, California, along the North Fork Stanislaus River. Built in 1910, this rockfill dam stands at 36 feet high and spans 1142 feet in length, with a storage capacity of 3283 acre-feet. The primary purpose of Union Main is hydroelectric power generation, with additional benefits for recreation and water supply.

Managed by the Federal Energy Regulatory Commission, Union Main is regulated at both the state and federal levels, with regular inspections to ensure its safety and compliance with regulations. Despite its low hazard potential, the dam is considered to have moderate risk (3) and has an emergency action plan in place. The dam's surroundings offer a surface area of 215 acres for recreational activities, making it a vital resource for the local community.

Located in a picturesque setting near Dorrington, California, Union Main serves as a critical infrastructure for water resource management in the area. With its historical significance and multifaceted benefits, this dam continues to play a crucial role in supplying water, generating clean energy, and providing recreational opportunities for residents and visitors alike.