Basin and Range Region
Basin and Range Region:
The "Great Basin" that Great Basin National Park is named after extends from the Sierra Nevada Range in California to the Wasatch Range in Utah, and from southern Oregon to southern Nevada. This is an area where no water drains to an ocean, but drains inward. As big as it is, the Great Basin is only part of an even larger region called the Basin and Range province that extends down into Mexico. The landscape around Great Basin National Park is a good example of what is found throughout the Basin and Range province - long mountain ranges separated by equally long, flat valleys.
Great Basin National Park encompasses most of the South Snake Range. The bulk of the rocks exposed in this range are formed of sediments like sand, mud and limey ooze (silt and clay particles mixed with calcium carbonate) that were laid down on the bottom of a shallow sea during the late Precambrian and Cambrian (around 560 million years ago). As layers accumulated upon layers, the sediments were turned into sedimentary rock. Sand lithified into sandstone, mud into shale, and limey ooze into limestone.
The rocks in the park were further changed during a mountain-building event that occurred around 200 million years ago during the Mesozoic Era. This event, the Sevier Orogeny, pushed layers of rock on top of each other, doubling the thickness of the crust. The layers at the bottom of the stack were metamorphosed slightly - sandstone changed gradually into quartzite, limestone to low-grade marble. Magma rose from deep within the Earth and pushed its way up into these layers. It did not come to the surface, however. Staying underground, it cooled to become granite. Where this hot magma was intruded, the surrounding rock was metamorphosed slightly more.
After all of this activity, the region still did not
resemble the present landscape. The modern basins and
ranges began to appear only within the
last 30 million years or so, during the
when the Earth's crust in this area began to stretch
in an east-west direction. Bedrock
nearest the surface reacted to the crustal stretching
by breaking into immense blocks several miles wide,
tens of miles long, and thousands of
feet thick. Many of these blocks fractured and the pieces
tilted and spread out like a row of odd-sized
books sliding out of place on a shelf.
The remnants of these broken blocks lie beneath the sediment
in the basins. Other blocks remained relatively intact and now form the
mountain ranges. Because stretching is in an east-west direction,
these ranges line up in a north-south direction.
The South Snake Range was
to see even more change. The younger unmetamorphosed layers of
rock on top of the range slid off of the older metamorphosed rocks in a
southeasterly direction, on a very low-angle fault line called a
decollement. This event makes the South Snake Range a metamorphic core
The end of the Cenozoic Era witnessed more
into the park, as well as
colder climates that further shaped the