Oldest Yosemite Rocks

A few miles below El Portal on Highway 140, a roadside sign identifies the oldest (metamorphic) rock in the Yosemite Region.  Since this is outside of the National Park, tourists, over time, have frequently broken off pieces of shale thinking that was the oldest–but not quite true!  Across the road, in the bottom of the Merced River bed, lies the real outcropping of the oldest rock, highly polished by millennia of river washing, impossible to break off a piece.  The best approach is to photograph it, but that’s really only possible in late summer, when the river flow is low.

Roadside Information Sign
The highly altered layers of ancient metamorphic rock, oldest in the Yosemite Region