Vonsen

About Vonsen

The primary purpose of Vonsen is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by Mary Volpi (private). It impounds the Tr San Antonio Cr near San Antonio.

The dam stands 35 feet tall and stretches 402 feet across, creates a reservoir covering 9 acres, has a maximum storage capacity of 70 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1951, the structure is well into its service life at over 50 years old.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 12/11/2025.

At 35 feet, this dam is taller than 82% of dams nationwide.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The California dam safety program can provide more specific information about emergency planning for this structure.

Search for dams near your address to see all dams in your area with hazard classifications and safety data.