When you hear the words “Great Basin,” you probably picture a bowl-shaped depression rimmed by mountains. While not exactly the case, it is true that the drainage system of Great Basin, a part of the greater Basin and Range province, has no outlet to the sea.

Geologic map of Great Basin National Park / NPS file

None of that rain or snow that falls in the area will ever flow into the ocean. So, this basin does, in a way, hold onto the water like a bowl or depression would, until that water evaporates back into the atmosphere.

What is basin and range?

Extending from the Sierra Nevada Range in California all the way down into Mexico, is a series of long mountain chains (the ranges) separated by a series of long valleys (the basins). Great Basin National Park encompasses most of one of these basin-and-range areas called the South Snake Range.

Most rocks you will see in this national park are sedimentary and metamorphic. What’s the difference? Sedimentary rocks come from sediments (sand grains, mud grains, clay particles) that were cemented together with a “glue” like silica or calcium carbonate. Metamorphic rocks resulted from immense heat and pressures (magma and mountain building). These processes changed (metamorphosed) such sedimentary rocks as shale into slate, limestone into marble, sandstone into quartzite. This occurred some 30 million years before the modern basins and ranges even appeared.

The commencement of this basin-and-range-building began when the Earth’s crust started stretching in an east-west direction, triggering the land to crack, buckle, fracture, and break into blocks thousands of feet thick and tens of miles wide and long in a north-south direction. Some of these blocks were ultimately buried beneath the earth, while others created the mountain ranges we see today, in between those flatter areas which became the basins.

During creation of these basins and ranges, other geologic processes occurred. Unmetamorphosed sediments slid off or were eroded from the tops of those mountain ranges, exposing more metamorphic rocks from beneath. Faults formed to move things up and down. Magma continued pushing granite intrusions through the existing rock layers.

A colder climate heralding the Ice Age 26,000 – 15,000 years ago pervaded the area. Glaciers scoured and sculpted the mountain ranges, creating such landforms as cirques like the one beneath Wheeler Peak, home to the last glacier in Nevada.

Great Basin is not finished with its evolution. It’s still geologically active. There are still earthquakes, faults, basin widening, mountain building, erosion, and all the other textbook geologic processes that originally created this Basin and Range province within which sets this national park.

For a far more detailed look at Great Basin’s geology, you can download and read the 2014 Great Basin National Park Geologic Resources Inventory Report.