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Las Vegas hosts NASCAR for a weekend every year, usually in March. The race draws about 150,000 race fans to the city. Many cheer for Kurt and Kyle Busch, natives of Las Vegas. Aside from NASCAR, the speedway hosts many other racing events throughout the year.
If time permits, and you don't mind watching a movie on your vacation, consider a visit to West Wind Drive-in; especially if visiting from out of the country where drive-ins are infrequent. And for an added bonus; it's normally a double-feature, so you get two movies for the price of one.
Home base of the air demonstration squadron United States Air Force Thunderbirds among others, the base is open to the public during airshows. Other than that, you can see military aircraft taking off and landing from a distance.
For the more serious fossil bed hunter (see Floyd Lamb below for more accessible viewings).
A pleasant oasis with ponds and tules and also the Tules Spring Ranch with some roaming peacocks and Pleistocene fossil exhibits.
Though not regularly visited, this is actually the largest national wildlife refuge in the lower 48 states. Coincidentally, it overlies part of the Nevada Test Site, so you can't just wander too willy-nilly, although the latter is quite distant. But this refuge's visitor center and trails will introduce you to aspects of the Mojave Desert ecosystem that are framed by some rather tall desert peaks, with a chance to see bighorn sheep and other species and even a yucca forest if you hike far enough.
CSN Planetarium
It's not on par with L.A.'s Griffith Observatory or Chicago's Adler Planetarium, but this planetarium and observatory can still help give an understanding to the skies and open space beyond. There's also an adjacent astronomy store that's open during the show times. Be aware, however, that chairs do not lean back, so there is a lot of looking up on your part.