It’s nothing but miles of barren, hostile, rocky desert and unnavigable mountains in every direction. His description is accurate.
The south side of the dam is attached to Arizona. Hardly the "middle" of the Nevada wilderness. Of course, the entire state is wilderness, with a few relatively tiny pockets of civilization, plus Reno and Las Vegas. ;-)
Almost all of Nevada is barren hostile rocky desert, but Hoover Dam is nowhere close to the middle of Nevada. His error was somewhat minor, but ignores Arizona. A more accurate description would have been; In the middle of the barren regions of the southwest on the Arizona-Nevada border.