The September 2007 issue of Wired includes an advertising supplement (pdf) built around a story on the A.D. Edmonston Pumping Plant, the centerpiece of the California State Water Project, which is the system by which water is brought from northern California down to L.A., San Diego, the San Joaquin Valley. The project is - as they say - an engineering marvel, and the pumping plant is the most marvelous part of the project, responsible for pumping zillions of gallons of water up and over a mountain range north of L.A.
Reading the story, though, all I could think is, "Holy crap: what a target for a truck bomb." Disabling the plant would apparently deprive much of Southern California of water, and though I'm sure there are some redundancies built into the CSWP, it sure sounds like the Edmonston Plant is the critical link. I suppose it's a commonplace by now, just a few days short of six years since 9/11, but really: hasn't al-Qaeda won some sort of victory when "what a great target for terrorists!" is a default reaction?