Wonder Stone at Grimes Point EarthCache
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Wonder Stone at Grimes Point
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The terrain in this area consists of low desert hills. The elevation is 4,048 feet. The site is found a little over a mile down Grimes Point Road, a dirt road, making it easily accessable.
Find out the origin of the red-orange-brown banded polished rounded stones on the ground in this area!
Nevada Wonder Stone is a volcanic rhyolitic air-fall tuff, material ejected from a volcano an estimated 12 million years ago. This rock was altered by geothermally heated water that deposited pyrite (FeS2) and quartz (SiO2). Over time, rainwater penetrated the rock and oxidized the pyrite to form red bands of hematite (Fe2O3) and orange and brown goethite (FeO(OH) called liesegang banding. Pieces of rock were broken from these outcrops by erosion and streams carried them to the shore of ancient Lake Lahontan, a vast body of water that once covered 8,500 square miles an estimated 13,00 years ago. The wonder stones are those pebbles that were tumbled and polished by the streams and wave action along the shores of ancient Lake Lahontan during this time. The wonder stone is, therefore, igneous (volcanic), sedimentary (laid down in sediments), and metamorphic (changed by hot water).
Ancient Lake Lahontan is an extinct lake in western Nevada and northeastern California that is thought to have been formed by heavy precipitation caused by Pleistocene glaciers. Along with Lake Bonneville, it occupied a large part of the Great Basin region. The depth of the lake is estimated to be about 900 feet (290 m.) at present day Pyramid Lake and 500 feet (150 m.) at present day Black Rock Desert. During the most recent glacial period, Lake Lahontan would have been one of the largest lakes in North America.
Climate changes around the end of the Pleistocene epoch led to the gradual disappearance of Lake Lahontan. As the waters abated, the lake broke up into a series of smaller lakes that dries, leaving only playas such as the Black Rock Desert, Carson Sink, and Humboldt Sink. Walker and Pyramid Lakes are the only present day remnants of the ancient Lake Lahontan. (Present day Lake Lahontan is actually a reservoir fed by the Carson and Truckee Rivers.)
TO LOG THIS EARTHCACHE, POST A PHOTO OF THE SITE ON THE CACHE WEBPAGE AND ANSWER THE FOLLOWING QUESTION:
To the north and east of this site you see
a) pinion pine forests.
b) a rhyolitic volcanic plug from the ancient volcano that was the probable source of the wonder stone.
c)horizontal benchmarks; stranded edges of ancient Lake Lahontan made by wave action.
d) b and c
You are standing on/in
a) a gravel pit.
b) a hill.
c) a ridge made by an ancient lava flow.
d) a playa.
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Treasures
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