Here we are about 1.1 miles outside of Nederland, looking north
at Mt. Audubon (13,233 ft). It is a beautiful late summer morning.
There's not a cloud in the sky.
We have Ogden Tweto's Geologic Map of Colorado with us. According
to it we are traveling through a region of Precambrian biotitic
gneiss, schist, and migmatite. These metamorphic rocks range in
age from 1.7 to 1.8 million years old and are derived mostly from
About 3.6 miles from Nederland we stop along side this roadcut.
The rock appears shiny and a little green. We
think this must be some of the schist we read about. The regular
platy fractures are really spectacular and seem to be caused by
the flat-faced sheets of mica. There is quite a bit of what appears
to be iron staining on these rocks, too. What we thought was especially
interesting is a seam of a black, shiny rock running through the
cut. We took a hand sample with us and, if our Audubon Field Guide
can be believed, the specimen is amphibolite. I would have though
that the amphibolite would be harder than the surrounding schist
At about mile 6.1 we pull off the road for a truly "Kodak®"
moment. The left edge of the road just drops away and we find ourselves
looking out upon an enchanted landscape of granite pinnacles. It's
hard to explain, but I feel as though I'm looking through a stereopticon.
The sense of depth seems artificial. I'm sure it has something to
do with the feathery appearance of the fir trees.
Consulting our geologic map, this granite appears to be Precambrian
in age (1.6 to 1.7 million years). You can see how the edges of
this formation have spalled away, giving the rocks a rounded appearance.
Reluctantly we get into our van and take off. We want to get to
Brainard Lake in time to cook some lunch.
about 6.2 miles we stop to take this picture of a pegmatite. On
close inspection it seems to be slightly pink. We break off a hand
sample and noticed the perfect cleavage. According the Audubon Guide
it is orthoclase feldspar.
We've seen these features all along our way, crisscrossing the
schist, gneiss, and granites. Some of them are feldspar, others
are quartz, still others are a mixture. These pegmatite may have
forced their way up through the fractures in the the rocks as recently
as between 24 to 29 million years ago.
At mile 7.5 we stop and take this picture of this highly metamorphosed
looks like the batter for a marble cake and it is really pretty.
A hand sample shows that it is composed of mica, hornblende, quartz,
feldspar, and a little biotite.
Most of the rocks in this area originally were shale, siltstone,
and sandstone, along with some volcanic rocks deposited about 1.8
to 2 billion years ago in an ancient sea.
Between 1.7 and 1.6 billion years ago, these sedimentary rocks
were caught in a collision zone between sections of the Earth's
crust called tectonic plates. These rocks, then in the core of an
ancient Proterozoic mountain range, were recrystallized into metamorphic
rocks by enormous heat and pressure resulting from the collision.
The shale, which contained mostly clay minerals and some very fine
sand and silt, was converted into biotite schist. The layers with
more sandstone were converted into biotite gneiss.
At the town of Ward we turn west and head up to Brainard Lake.
It's a steep climb, going from 9250 feet to 10,300. We climb out
of the Precambrian formations and into Quaternary glacial deposits.
Everywhere you look you see boulderseach different from the
one next to it.
This picture is taken on the shore of Brainard Lake, looking west
at the Indian Peaks. We see Audubon, Toll, Pawnee, Shoshoni, Navaho,