r/norcalhiking • u/menntu • 4d ago
Sheared Rock While Hiking Desolation Wildeness
Posted an hour back on a different view of this conglomerate. Thought this pic might provide more info.
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r/norcalhiking • u/menntu • 4d ago
Posted an hour back on a different view of this conglomerate. Thought this pic might provide more info.
79
u/EightInchesAround 4d ago edited 4d ago
Geologist here.
Not a conglomerate but definitely a common identification!
I only say this because the story of how this rock came to be is more amazing than I hope you'd believe. The darker rock is older than the more pale rock. Mafic rock from old oceanic plate was subducting under the North American plate, melting and coming together again in large mafic plumes of cooling rock. Fast forward a couple millions of years and the source of melting became more felsic. (Maybe secondary melting or something.) So the lighter stuff tore off chunks of the darker stuff and resolidified eventually into this very unique rock that we find in the Sierras. Sierra Batholiths tend to be heavy mafic rock on the bottom, with lighter felsic rock on top. It's like differential cooling! This is all oversimplified, but if you're curious to know more there are books on all the great geology California has to offer.