Mysterious hole on the ocean floor off California's coast

On the sea bottom off the coast of central California lies a vast field of mysterious pockmarks. 

The field spans about 1,300 square kilometers and there are approximately 5,200 of these strange pits, which on average measure about 175 meters and 5 m deep.

No one knows how these mystery holes appeared, but they likely made their first appearance 400,000 years ago, according to research. 

Coordinates: 33°39'17.76"N 118° 7'5.82"W 
Vast field of mysterious, perfectly circular holes dot the seafloor off California's coast.