Upper 4s Ranch, located in Del Mar, California, is a privately owned dam on Lusardi Creek with a primary purpose of water supply for irrigation. Built in 1927, this arch-type dam stands at 28 feet high and has a storage capacity of 48.3 acre-feet. With a low hazard potential and satisfactory condition assessment, Upper 4s Ranch plays a crucial role in water resource management in the region.

Managed by the California Department of Water Resources (DWR) and subject to state regulations, inspections, and enforcement, Upper 4s Ranch is a key infrastructure for maintaining water supply and ensuring the safety of dams in the area. The dam's last inspection in June 2020 confirmed its sound structural integrity, further reinforcing its importance in the local water management system.

With its historical significance dating back almost a century and its ongoing role in supporting irrigation and water supply needs, Upper 4s Ranch serves as a vital resource for the community. As water resource and climate enthusiasts, understanding the infrastructure and management of dams like Upper 4s Ranch is essential for sustainable water management practices in California.