Wednesday, September 22, 2010

The Great Basin

The Great Basin is an endorheic watershed, if you know what that means… for that matter, its still one even if you don't know what it means.

In fact, it's the largest area of contiguous endorheic watersheds in all of of North America! And, is particularly notable for both its arid conditions and its widely varied Basin and Range topography.

The North American low-point, at Badwater Basin, is less than 100 miles away from the contiguous United States' highpoint, at Mount Whitney summit.

Endorheic Basin

"Endorheic" is one of those high-falutin' Greek based words (meaning "within" and "to flow"); which, to us normo-falutin' people, translates into: "a closed drainage basin which retains water and allows no outflow to other bodies of water such as rivers or oceans." It may also be called an "internal drainage system."

Normally, water that finds itself in a drainage basin eventually flows out through rivers or streams or permeable rock – ultimately winding up in an ocean.

An endorheic basin… not so much. In such a basin, the center is lower than any possible route to the ocean, and to top it off the rock isn't all that permeable. So any water that gets in pretty much has only two options: evaporation and seepage.

It shouldn't be too much of a surprise then that the bottoms of such basins are typically occupied by a salt lake or salt pan – and this one has a doozy! The Great Salt Lake, the vestigial remnant of prehistoric Lake Bonneville, is up to EIGHT times as salty as an ocean and can only be inhabited by Brine Flies and Brine Shrimp.

The Great Basin watershed spans several physiographic divisions, biomes/ecoregions, deserts, and metropolitan areas in the states of Oregon, Idaho, Wyoming, California, Nevada and Utah. And, in addition to being the ancestral homeland of the Great Basin tribes, was the 1849 location of the provisional State of Deseret which is now known as Utah (only a shadow of its former self.)     [For a free Google Earth file of this geographical feature see: The Great Basin]

Will the REAL Great Basin please stand up?

Unfortunately, or fortunately, "The Great Basin" is such a nifty sounding name that it is used for several different areas, all having similar, but different, borders.

There's the "Great Basin Desert" [black on the graphic] and the "Great Basin Watershed" [purple] and the "Great Basin and Range" [teal], each increasing in the size of its borders and each sporting its own cadre of "professionals" who shorten the moniker to simply: "The Great Basin."

The Great Basin Desert is the largest U. S. desert, covering nearly 190,000 square miles between the Sierra Nevada's (west) the Rocky Mountains (east) and the Columbia Plateau (north).

Due to its northern latitude and higher elevations (>3,000 feet) it is known as a "cold desert." In fact, it is precisely this difference in temperature/rainfall (and the resultingly different flora/fauna it produces) which enables the desert gurus to split this desert from its neighbors the Mojave and Sonoran deserts to the south(ish).

Additionally, this desert's 7-12 inches of annual rainfall (often snow), is more evenly distributed throughout the year than in the other three North American deserts.

Other distinguishing characteristics of this desert are: Playas – due to its recent geological activity; low and homogeneous vegetation – including miles of a single dominant species of bush; and no yuccas and few cacti – Big Sagebrush, Blackbrush, Shadscale, Mormon-tea and greasewood instead.

You may also want to include the Colorado Plateau (northeast Arizona, and four-corners of Utah, Colorado and New Mexico) in the Great Basin Desert – or not! You might want to call it the separate "Navajoan Desert" – or not! Or, not even call it a desert. People don't seem to be able to make up their minds. Even though it has large barren areas its got lots more juniper and pinyon trees cause it's higher.

The Mojave Desert, immediately to the south, has Yucca's and the Great Basin doesn't so there must be something different there. Even further south the Sonoran, known to all other North-American deserts as "mama," has different lizards and apparently no top on their thermometer.

What On Earth Happen?

Taking the James Mitchner approach and beginning at… well… the beginning, it all began under water.

If you want to sound good at parties you can claim that "sediment built up over thousands of years between two bounding undersea ranges and created a relatively flat lacustrine plain which would later be named the Great Basin after it drained.

Pleistocene lakes Bonneville, Lahontan, Manly and Mojave – not to mention Great Salt Lake, Utah, Sevier, Rush and (yes) Little Salt lakes – all have this prehistoric entity on their pedigree chart.

Lake Bonneville became as large as Lake Michigan is now, covered ten times the area of Great Salt Lake, was over 1,000 feet deep and spanned the Great Ice Age – 32,000 to 14,000 years ago.

About 16,800 years ago a huge ice-dam broke flooding a large portion of the lake out through Idaho's Red Rock Pass.   Climate changes and a couple similar breakages fairly dessicated the thing into the lakes that are left.   And now they are even claiming that evidence suggests the thing may have evaporated and reformed as many as 28 times in the last 3 million years.

After the dinosaurs left, Native Americans (the Great Basin tribes) began moving into the area (known on the cocktail circuit as the "Paleo-Indian habitation") – around 10,000 B.C. – and continued at least through 1,000 A.D. when the "Shoshonean peoples" entered fashionably late.

Archaeologists have found "houses" around Lake Lahontan dating from back at the end of the ice age when its banks were lapping 500 feet up the slopes of the mountains.   And for at least several thousand's of years the Great Basin's official language was Uto-Aztecan from the Shoshone, Ute, Mono and Northern Paiute tribes.

An archaeologist is the best husband a woman can have. The older she gets the more interested he is in her.”
Agatha Christie
Present day exploration of the Great Basin began in the 18th century. Benjamin Louis Eulalie de Bonneville (1796–1878), a fur trapper, explorer and eventual officer in the U.S. Army, went offroading to the northeast in an 1832 expedition. The geologist G. K. Gilbert came along after him and named Lake Bonneville.

The United States acquired control of all the area north of the 42nd parallel via the 1819 Adams–OnĂ­s Treaty with Spain; the 1846 Oregon Treaty with England; and the 1848 Mexican Cession.

The 1848 California Gold Rush had its European immigrants crossing the Great Basin on the California Trail along Nevada's Humboldt River through Carson Pass in the Sierras.

Then, as the first American religious settlement effort, the Mormon provisional State of Deseret was established in 1849 and eventually became the present day states of Utah and Nevada.

The Oregon Territory was established in 1848, the Utah Territory in 1850 and the 1860-61 Pony Express stations connected the Great Basin between just west of Lake Tahoe and northeast of the Great Salt Lake.

The rest… as they say… Is History!

Learn A Little More

There is an excellent source for maps of the Great Basin Watershed on the web, namely: Elevation Derivatives for National Application (EDNA) Watershed Atlas. And there are even two versions: the KML (Google Earth) and HTML (web) versions.

The EDNA home page, where you can obtain both formats, is at:,
An index for KML files of all US watersheds is at:,
And the KML file for just the Great Basin is at:


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