More than 1,000 oil and gas wells operate in relative secrecy in Los Angeles, behind tall fences or other clandestine structures. Most sit feet from hospitals, daycare centers, schools and homes.

That means more than a half million county residents live less than a quarter of a mile from a drill site. Many have no idea.

As the health impacts from drilling become clearer, the push to expose these sites, establish wider buffer zones and, ultimately, shut them down becomes more urgent.