This entry is part 7 of 10 in the series Nevada Theme Month

The Great Basin

Most Americans, at some point during primary schooling, learn about an important hydrological boundary known as the Continental Divide.

This imaginary line follows the mountains from Alaska, through Canada, down the Rockies, and into Mexico. Technically, the divide does not stop at the edge of North America but splits South America, too. We learn that water on one side of the line flows to the Atlantic, while water on the other heads to the Pacific.

In the United States, the Missouri and Mississippi system is so large that water from a vast majority of the area ends up in the Atlantic Ocean.

The concept is simple, so most discussions on where water goes end after introducing the divide.

It’s easy to overlook a straightforward but important question: does all water flow to the Atlantic or Pacific? Geographers consider the Gulf of Mexico, Hudson Bay, and the Labrador Sea, as seen in the graphic above, part of the Atlantic system, so there’s no trick involved in that aspect of the query. The blue, green, pink, and yellow lines represent smaller divides that separate, for example, water heading to the Gulf of Mexico or the Atlantic Ocean proper.

However, the map above features a strange circular section, for lack of a better term. The brown line defies the conventional wisdom about the Continental Divide. This area is known as the Great Basin, and water that falls in this region doesn’t end up in the Pacific.

The Great Basin does not violate the larger point of the divide (i.e. the water does not magically hop over the Rockies and travel to the Atlantic); instead, water in the Great Basin obeys the Las Vegas Principe: what happens in the Great Basin stays in the Great Basin.

Covering nearly all of Nevada, half of Utah, and parts of Oregon, California, Idaho, and Baja Mexico, the Great Basin is an endorheic watershed. This pedantic term means that water does not outflow to another area. Endo- is a prefix meaning “internal”, and rheo comes from Ancient Greek, meaning “to flow.”

Though much of the Great Basin is desert, its endorheic attribute does not mean it lacks water. Many lakes serve as sinks for the water of the region, including Great Salt Lake, Pyramid Lake, and Lake Tahoe. The basin even has rivers, such as the 350-mile Bear River, which drains into Great Salt Lake, and the Humboldt River, a massive drainage system that ultimately dumps its water into the Humboldt Sink, an intermittent dry lake bed.

Water that does not journey to a lake either evaporates or finds its way into aquifers, supplying the water table.

The Great Basin contains some of the most iconic desert landscapes in the world, including Death Valley National Park and Joshua Tree National Park.

Ironically, most of the precipitation that falls in the Great Basin does so in the form of snow.

If snow falls in this unique territory, it has several options when it melts: evaporate, go underground, or head to a lake. If it wants to join its brethren in the Pacific Ocean, it will need to take the evaporation route and trust the water cycle because no river will take it out of the Great Basin!