Vonsen is a private water supply dam located in Petaluma, California, along the Tr San Antonio Creek. Built in 1951, this earth dam stands at a height of 35 feet and has a storage capacity of 70 acre-feet. Its primary purpose is to provide water for irrigation and domestic use in the surrounding area. The dam is regulated by the California Department of Water Resources (DWR) under the Safety of Dams program, with regular inspections to ensure its structural integrity.

Despite its satisfactory condition assessment and significant hazard potential, Vonsen has not been modified in recent years and lacks certain emergency preparedness measures such as an Emergency Action Plan (EAP) and inundation maps. The dam is under state jurisdiction and is subject to state permitting, inspection, and enforcement. With a drainage area of 0.2 square miles and a surface area of 9 acres, Vonsen plays a crucial role in water resource management in Marin County.

Overall, Vonsen serves as a vital water supply infrastructure in the region, contributing to irrigation and domestic water needs. As a privately owned dam, it is essential for the owners to adhere to regulatory requirements and ensure the dam's safety and functionality. With its proximity to the San Francisco District of the US Army Corps of Engineers and under the oversight of the California state regulatory agency, Vonsen remains a key component of water resource management in the area, highlighting the importance of sustainable water infrastructure in the face of changing climate conditions.