It an amazing thing really. It takes place in hammertown, USA. A place that for 50 weeks a year is a desolate desert dry lake bed, but for 2 weeks it transforms into 50,000 people creating a city in the middle of no where.
You can go to google maps and type in king of the hammers and the location will come up, basically south of Barstow CA and west of Hesperia.
Just last week jalopnik called it one of the top 10 hardest races in the world.