Del Puerto Canyon is located at the eastern edge of the Diablo Range and next to the town of Patterson.  The reservoir would be formed by pumping and storing water from the Delta-Mendota Canal in wintertime in Del Puerto Canyon behind four earthen dams, which would be released as needed over the summertime. Whatever water flows down Del Puerto Creek will also be retained in the reservoir, but 99% of the stored water will come from the canal. It's primary purpose is for selling water to large-scale agribusiness down south by Fresno that produce goods for export and not potable water for households. The approx. $500 million-$1.1 billion reservoir’s maximum capacity is to be 82,000 acre-feet or 27 billion gallons of water (roughly 5-6% of Sites Reservoir's capacity once it's built and 30% of Los Vaqueros Reservoir once that's expanded). The reservoir would extend past Graffiti and Owl Rocks and the creek that the community enjoys so much (link to a page with a map by Save Mt. Diablo). Two of the four dams are of significant size and present dangerous problems to the community of Patterson.  

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The main dam would face I-5 just north of the Patterson entrance to the freeway and cut off Del Puerto Creek, which is a natural source for local groundwater recharge and has been cited by sportfishing groups as an important source of breeding gravel for downstream sturgeon populations.  The main dam would be 260 feet high and 1,409 feet long, roughly speaking, the height of a football field stood on end, and fourteen football fields long. This dam will close off what has been historically known as Del Puerto, meaning "The Door". The second large dam facing Patterson will be located along Del Puerto Canyon road and will be 150 feet high and 1,300 feet long. 

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The dams are earthen because the canyon is not solid rock but is subject to movement, and earthen dams can settle into unstable ground as it moves. The typical basic design of earthen dams includes standard safety features that proponents hope will protect the dam against failure; as the old saying goes, “hope springs eternal” – but no guarantees!  Many Patterson residents are concerned about the possibility of flood risks and impacts to housing, insurance, etc., related to living near this project, the impacts to the proposed city park by the Gateway Rocks within the project's footprint, and the loss of valued natural, recreational, and cultural resources along Del Puerto Canyon Road.

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