[The following information is from a remote sensing tutorial published by NASA.]
Major C.E. Dutton, an early explorer of the American West, described these mountains as they appeared on a map as resembling "an army of caterpillars crawling northward out of Mexico".
Hmm, I see what he's saying. Below is a color - coded relief map (relief: the ups and downs of the landscape) of NV.
The mountains are uplifted parts of older continental crust. This area was being pulled apart, slowly, and the pieces in-between sank lower. The valleys are filled with a lot of sediment that has eroded from the ranges and partially filled them up. This is what the area looks like from the air.
Some of these peaks are significant. Wheeler Peak in Great Basin National Park is about 13,000 ft (4000 m) tall. What little rain or snow there is falls on these peaks and so the heights are green with pine trees, even white with snow. It is quite different from the dry, hot, desert valleys in between!
There is a wonderful part of the East Humboldt Range where erosion had sculpted the ridges in amazing ways, and the ridge is so thin that there is a hole right through it! This, of course, is called the Hole-in-the-Wall (or Lizzie's Window), near Hole-in-the-Wall Mountain. Please see this website for hiking in the area. The photos are amazing, but copyrighted, so I am not going to reproduce them here.
Las Vegas is way to the south of the state. Many areas in the middle of the state are very sparsely populated. With renewed gold mining in some areas in the north, population has grown somewhat.
Much more detail from about.com: http://geology.about.com/library/bl/maps/blnevadamap.htm
Nevada Bureau of Mines and Geology: http://www.nbmg.unr.edu/