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We found this while hiking at about 5,000 feet elevation in the northern Sierra Nevada.  It was in a drainage.  I am definitely not well-versed in geology or rock identification.  Maybe it's limestone?  What caused the holes and what might the white material within the holes be?  (Looks like over time the white material was worn away by water, leaving the holes?)

Thank you very much for your time.


Hi Jenny,
Your question sounds like you meant for a picture to accompany the question but I didn't get it.  Perhaps you could send me an image with an object in it for scale, a coin works just fine.  Otherwise I'll just be guessing.  If it's gray it certainly could be limestone.  The holes filled with white material make me think of volcanic material with mineral-filled vugs.  However, the Sierra Nevada Range is mostly granitic.  Not too likely to have limestone there, and there might be some volcanics but it is very minimal. Granite can be weathered and the white material could be quartz.  Quartz is very common in granite.

All conjecture.  Without a picture I'm just waving my arms.  If you'd like, resend the question, with an image, and we'll go from there.

One thing you can try; limestone is very reactive.  If you can get some hydrochloric acid (a pharmacy or they clean pools with it), pour a few drops on the rock.  If it's limestone it will fizz.  HCL may be hard to get, vinegar will also make it fizz a little bit.  If you can scratch the rock, put a few drops of vinegar on the scratch.  If it fizzes you have limestone.

Hope this helps.


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C. Robert Reszka, Jr.


I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.


I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Michigan Basin Geological Society

Decade of North American Geology.
Bedrock Geology of Michigan

BS Wayne State University

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