Big Rock Ranch, located in Nicasio, Marin County, California, is a privately owned Earth dam built in 2002 primarily for water supply purposes. The dam stands at a height of 45 feet and has a maximum storage capacity of 91.3 acre-feet, serving as a vital resource for the surrounding area. Situated along the Nicasio Creek Tributary to Lagunitas Creek, the dam plays a crucial role in ensuring water availability for both recreational activities and domestic use.

Despite its high hazard potential, Big Rock Ranch has been assessed to be in satisfactory condition, with regular inspections conducted by the state regulatory agency, Department of Water Resources (DWR), Safety of Dams. The dam's emergency action plan (EAP) was last revised in January 2021, emphasizing the importance of preparedness and risk management measures. With a drainage area of 0.52 square miles and a surface area of 7 acres, the dam contributes significantly to the water supply infrastructure in the region, highlighting its critical role in water resource management and climate resilience efforts.

Managed by private owners, Big Rock Ranch serves as a key asset in maintaining water security and supporting the local ecosystem. The dam's strategic location and design not only ensure adequate water storage but also contribute to the overall water management system in the area. With its strong enforcement, inspection, and regulatory measures in place, Big Rock Ranch stands as a testament to effective dam operations and underscores the importance of sustainable water resource management in combating the challenges of climate change.