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most of the national parks in the United
States were founded on their geology
Yellowstone displays volcanic features
the Grand Canyon shows millions of years
of sedimentary history and here in
Yosemite the geologic story is primarily
one of granite
granted is what's known as an igneous
rock which means it's born of fire it
cooled and solidified from magma or
molten rock and when magma erupts on the
surface we think of it as lava basically
granite started off as something similar
to that
it was red-hot fluid rock but instead of
making it up to the surface and erupting
as lava in a volcano it stayed many
miles below the surface and cooled there
very slowly over thousands of years and
because it cooled so slowly it allowed
very large crystals to form it's a very
coarse-grained rock and that's the key
to its strength this rock spent a long
time at high temperatures cooled very
slowly and that allowed a lot of the
cracks to be annealed out of it making a
very strong Rock so the glaciers had a
hard time moving it and that's what
allows you to carve the kind of
landscape that you can see over my
shoulder here granite is among the
toughest rocks on the planet I mean it's
very very strong stuff so when glaciers
are moving through here they certainly
were able to erode and sculpt the
landscapes um but a lot of the domes the
smooth ridges that we see up here in the
high country they're really a testament
to the fact that glaciers weren't able
to do a lot of eroding of this landscape
one of the things that makes us emiti
such a great place for us as geologists
to work is that Nature has taken these
rocks and polished them for us and so we
can come out here and literally crawl
around on our hands and knees looking at
beautifully polished specimens that in
places are polished almost as well as a
commercial company would polish up your
kitchen countertops for you so we can
see the relationships among these
minerals we can see into the guts of
what was a magma chamber and see what
was going on then frozen in time for us
every visitor to Yosemite I think
experience is granted in some way I mean
you can't hardly not experience granite
in a park like this where most of what
you see is granted and that can range
from just taking a quick stroll off the
side of the road to a place like Olmsted
point to taking the hike up Half Dome up
to the
on it too spending four or five days
climbing up El Capitan I think more than
most visitors rock climbers have a
really good sense for granted
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climber's take advantage of lots of the
geologic features of the granite such as
these feldspar knobs that stick out such
as the occasional cracks such as some of
the dark blobs of different kind of rock
in the granite that weather out that you
can use for hand holds or footholds okay
so what minerals you got so far
biotite quartz and potassium rosa okay
what else might you expect ifs I got my
class it's a first-year seminar at the
University of North Carolina we come out
here every fall and we always bring them
in to Yosemite for at least a day
because it's an experience that everyone
needs to have as soon as possible in
their lives you know somebody is a great
place to just come learn more about
granitic rocks you'll see them
everywhere you can easily walk around on
them look at them closely and I think it
helps that you can be studying these
rocks in such an inspiring place you
know where the landscape just sort of
opens your mind up to trying to
understand it better when I walk around
here and look at the Granite's I think I
understand a lot about how most of the
features that I see formed I can see
cracks that filled with magma I can see
blobs of the dark magma that were caught
up in a lighter magma then we can
understand that by studying it by doing
chemical analyses by doing experiments
to try to duplicate some of these things
but there are a lot of features out here
that none of us understand
when you walk around on these glaciated
surfaces you can find a lot of really
unusual things some of them I think we
understand and some of them are great
mysteries I've been to this place maybe
half a dozen times and I really have no
idea how this formed it's one of the
weirdest things I've ever seen in a
granite same things like this is kind of
humbling I think we understand a lot
about the Granite's in Yosemite and how
they form and over what time periods
they form and so forth but you walk
around a corner you're in into something
like this and it's really humbling it
says there are a lot of mysteries out
there still left solve
I think a lot of visitors when they come
to the park they're not thinking about
geology per se but you know they're
they're here to experience this
beautiful place it's right here in the
core of Yosemite that we have the best
exposure of granite and that's also
where we have the most amazing
landscapes into our meadows in Yosemite
Valley they are a direct result of the
granite that's here
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