See the context of this sign.

Oldest Rocks of
Yosemite Region

These wrinkled and broken strata are the
oldest formations of the Yosemite Region.
They were formed in the sea on deposits of
mud, sand, and other material. Folding, breaking,
and change in texture resulted from
movements which produced the original Sierra
Range, now largely worn away.

In forming those ancient mountains, immense
masses of melted rock moved upward into the
earth's crust below the disturbed area. This
molten material cooled to form granite. The
granite may be seen in Merced Canyon immediately
above El Portal and in Yosemite Valley.

Across the Canyon from this point the river
has cut and polished these rocks, causing
the intensely folded layers to stand out
in bold relief.

Don't miss the rest of our virtual tour of Mariposa County in 5798 images.