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Devils Postpile National Park Geologic Story
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Other Geologic Features
Glacial erratics are boulders carried by ice from points upstream. They have been deposited in many places within the Monument, but are most abundant on the high granite hills and ridges west of the Middle Fork of the San Joaquin River. Many of the erratics are different from the rocks they now rest upon, and some are composed of metamorphic rock which occurs only north of the Monument. The erratics of metamorphic rock tell us that the ice carried them south from a distant source.
Mineral springs- some of them hot- occur within or near the National Monument. They are further manifestations of the recency of local volcanic activity. One cold, highly-carbonated spring flows out on a gravel bar on the west side of the Middle Fork of the San Joaquin River in Soda Springs Meadow, about one-tenth of a mile north of the Devils Postpile. Such springs often occur where gasses and water vapor are driven upward from hot areas deep in the Earth and combine with ground water near the surface to produce mineralized springs. At Soda Springs, iron present in solution in the acidic water oxidizes on exposure to the atmosphere and has stained the river gravel in the vicinity a reddish brown. A hot spring issues forth at Reds Meadow, just east of the Monument, further attesting to the continuing volcanic activity in the area.
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| Devils Postpile geology home |
Devils Postpile National Monument home |
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| USGS Geology in the Parks home | NPS Park Geology Tour home |
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http://www.nature.nps.gov/grd/usgsnps/depo/dpgeol12.html
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