Hoover Dam is one of the greatest engineering marvels of modern history. It’s just a short drive from Las Vegas and within the boundaries of Lake Mead National Recreation Area.
The Spring Mountains National Recreation Area, commonly referred to as Mount Charleston, is a great place to beat the desert heat of Las Vegas.
Glen Canyon National Recreation Area is a huge park surrounding Lake Powell. It covers 1,254,429 acres of mostly desert, with roughly ⅔ in Utah and ⅓ in Arizona.