From the Super Mario Wiki, the Mario encyclopedia
The Desert Kingdom is a large, sand and cactus filled area which has a large racetrack running through it. The Desert Kingdom appears in The Super Mario Bros. Super Show! episode "The Great BMX Race", where Mario and Luigi have a race against Mouser, Tryclyde and a Koopa Troopa through it.
Although a few buildings, a restaurant, and what could possibly be a junkyard are found in the Desert Kingdom, no inhabitants of it are actually shown.