So, that's how they do that! 25 million pounds of dirt is prepped for the Monster Energy Supercross race inside Sam Boyd Stadium

but you can see a much better video (that doesn't have an embed feature) http://www.reviewjournal.com/sports/motor-sports/watch-sam-boyd-stadium-become-supercross-track-under-2-minutes-video

the 15-year-old dirt of Sam Boyd Stadium, where veteran operators of front-end loaders, bulldozers and mini-dozers called skid steers maneuvered their earth-moving machines like ballerinas to create the obstacle bump-filled three-dimensional motorcycle course for the Monster Energy Supercross Finals make up the sport’s playing field, so to speak.

 Feld Motor Sports, based in Aurora, Ill., stores 550 truck loads of the dirt right outside Sam Boyd Stadium, where it’s used for other Feld events, such as the Monster Jam World Finals.

The same dirt is used time after time for Feld sport events at Sam Boyd Stadium. The dirt for the Monster Jam event is not removed from the stadium between the Supercross Finals and the Monster Jam Finals, but instead stored in the center of the venue because the stadium that’s managed by the University of Nevada, Las Vegas.

It takes trucks two days to transfer the dirt from outside the stadium to inside the venue, so arranging the schedule for both dirt track events, cuts considerable time and cost from set up for the 2nd event.

Immediately after the Monster Jam ends, crews begin pushing the dirt into a two-story-tall mound in the center of the stadium field to store it for preparation of tilling it and adding water to keep it soft, moist and usable for the Supercross, Prater said.

In 2006, crews did not move the dirt into the center of the stadium after the monster truck event. So, when the Supercross workers showed up a few weeks later to begin forming the dirt course in the shapes of table tops and camelback-like mogul bumps, they found dirt that “had settled like brick,” Prater said.

Nathan Swartzendruber, the event paddock manager, said an eight-inch base of dirt sits on two layers of plastic over the UNLV football field. Feld hires a company called Dirt Wurx, based in Monroe, N.Y. outside New York City, to move the dirt and set up the course.

Prater valued the dirt at $100,000-$180,000, noting that Feld tries to acquire dirt coming off construction sites.

http://www.reviewjournal.com/sports/motor-sports/down-and-dirty-heavy-equipment-operators-massage-dirt-position-supercross-event