Most people would never expect it, but Nevada ranks fourth in biodiversity in the United States. The reason is simple enough. Its range of elevations, climates, and deserts create hundreds of isolated ecosystems across the entire state.

Some species of wildlife are unique only to a single pool of water, including the Devil's Hole pupfish. Much less isolated, but also endangered, are bighorn sheep. Characterized by their muscular bodies, deer-like coats, and massive brown horns that curl in spiral fashion, the Sierra Nevada Mountains are home to all four subspecies including two of the rarest.

According to Exploring the Southwest Desert, one of these subspecies that lives in Nevada is even more rare than the Florida panther and the California condor. In fact, the article suggests it is the most endangered mammal in North America.

Spotting The Desert Bighorn.

Every year, as summer approaches, desert bighorn move closer to their meager water supplies, which include the Colorado River along the steep cliffs of the Black Canyon. And as summer presses on, they rest during the day in caves or under rocky overhangs.

Their natural tendency to climb steep terrain so they feel protected from predators is one of the reasons they have taken to the Black Canyon. (Bighorn sheep can use footholds as small as two inches to bounce from ledges as far as 20 feet.) Because they feel safe in this environment, spotting sheep from the Colorado River is one of the easiest and least intrusive way to catch a glimpse.

Currently, there is a licensed tour that transverses a 12-mile course down the Colorado River from the base of Hoover Dam in Nevada to Willow Beach in Arizona. While the river is one of the common area to see bighorn sheep, the tour includes a spot at one local park where an entire herd sometimes grazes on sweet grass.

Helping To Save Bighorn Sheep.

Bighorn sheep used to number in the millions across North America hundreds of years ago. But unfortunately, the entire population crashed to only several thousand in 1900.

They may have even gone extinct had it not been for the Arizona Boy Scouts who organized a state-wide campaign to save them in 1936. Later, the National Wildlife Federation, the Izaak Walton League, and the National Audubon Society joined their effort. Today, there are a number of organizations dedicated to supporting the conservation of bighorn sheep.

• National Wildlife Federation
• The Bighorn Institute
• Arizona Desert Bighorn Sheep Society
• Wild Sheep Foundation

The tour mentioned above also includes a "Discovery Tour" at Hoover Dam after the relaxing scenic river raft trip. For more information about the Black Canyon Colorado River Raft and Hoover Dam Tour or things to do in Las Vegas, visit TourGuy.com