Our group arrived about a half hour early when the only activity in the arena was the cowboy version of the Zamboni® machine that we city folks are used to seeing at the ice rink.
At the Cowtown Rodeo it's a long flat sled towed by two large quarter horses.
I'm not sure what good it does to the arena, since the dirt and mud looked pretty much the same after the sled had passed, but I suppose it's one of those rodeo traditions of which I'm not aware.