Rambling Rodericks travel blog

 

 

Mt. Jefferson (on the left) & Wheeler Peak (which looks lower from...

"Popcorn" on a stalagmite

"Columns", formed by joined stalactites & stalagmites, with popcorn

 

 

A shield separated from the ceiling

Shields

 


It's called the Great Basin. It's a vast region of sagebrush-covered valleys and narrow mountian ranges. The basins are bowl like areas between the mountains which lack drainage. Its streams and rivers mostly find no outlet to the sea, and water collects in shallow salt lakes, marshes, and mud flats to evaporate in dry desert air. It's not just one but many basins separated by mountain ranges which are roughly parallel, north to south. Another name for this area is Basin & Range. It extends from the eastern side of California's Sierra Nevadas to Utah's Wasatch Mountains.

Congress created Great Basin National Park, along the Nevada/Utah border, in 1986. It is a superb example of a desert mountain island. From sagebrush at its base through juniper and pine forests and even through groves of ancient bristle-cone pines, with alpine plants and many limestone caverns, including Lehman Caves, the glacial summit of Wheeler Peak soars at 13,063 feet, the second highest peak in Nevada.

We drove the 24 mile scenic road to the base of Wheeler Peak, and explored Lehman Cave with a guided tour. A unique feature of this cavern is what is called a "shield". Shields are the formation for which Lehman Caves is best known. Shields consist of two round or oval parallel plates with a thin medial crack between them. Water under hydrostatic pressure moves through thin fractures in the limestone. As it enters the cave passage by means of capillary action, the water deposits calcite on either side of the crack, building plates of calcite with a thin, water-filled crack between them.

Shields may be decorated with popcorn or helictites on the top and along the medial crack, and draperies and stalactites on the bottom. Sometimes the formation on the bottom plate gets so heavy it pulls the shield apart causing it to separate from the ceiling. Looking up from under them, I think they look like jellyfish.



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