Answer: Oil rigs
When most people think of Los Angeles, they think of Hollywood, movie stars, scenic boulevards, and the beautiful weather of Southern California. However, long before there was a Hollywood embedded in a thriving metropolis, there were oilfields.
Just because Los Angeles became one of the United States' most densely populated urban areas does not mean that all oil was ignored. Around the citizens of LA, many of whom do not notice the fact, there are nearly a hundred active oil wells. Hidden in four windowless office buildings, as shown here, these oil wells pump quiet (and secretly) oil from the depths of the city. So far, more than 1