American Association of Petroleum Geologists (AAPG)
The Toyokawa field is a small oil field, covering an area of about six square kilometers, located in northeastern Japan’s Akita Prefecture. The hillock area where the Toyokawa oil field is situated formerly was covered with natural asphalt (tar) deposits that had erupted from the subsurface. The current scenery resembles the famous La Brea Tar Pit in Los Angeles.
Toyokawa Field Yields Oil, Prehistoric Asphalt