Drug cartels have resorted to underground tunnels to avoid detection since security has become more stringent along the border.

Since 1990, about 170 tunnels have been discovered, the majority of them have been along California and Arizona’s border with Mexico. As a result, the U.S. border patrol will soon unveil an underground wireless robot equipped with camera to search underground networks.

The tunnels vary in terms of size and complexity, depending on who’s using them. While some can be extremely simple such as those dug by hand, others can be extremely sophisticated, including ventilation, lights, and supports for ceiling.

Those employed to construct rudimentary tunnels are miners who use hoes, shovels, jackhammers and picks to excavate soil which is transported out of the tunnel’s opening in Mexico. They normally old-fashioned tools like a compass to do their work.

However, cartels who want to construct sophisticated tunnels normally hire engineers as well as miners to build the tunnels. Those tunnels found near San Diego, Arizona, are good examples of sophisticated tunnels.

U.S. border officials have estimated the cost of more sophisticated tunnels to be between $2 million and $3 million.

Once a tunnel has been built, the smugglers use it to move guns and drugs as well as people who want to sneak into the U.S. Officials say that some traffickers are selective about what can move through their tunnels but most sophisticated tunnels are mainly used for moving drugs and guns across the U.S Border.

Marijuana is among the drugs that are mostly moved through the tunnels because it is bulky and riskier to move above the ground. In 2011, authorities seized about 32 tons of marijuana that was being moved across a 600-yard tunnel in the southern California. The tunnel was equipped with lighting, railcars and ventilation while the floor was lined with wooden planks.

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