Rocks Lab 3 Alexi Lindsay
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Colorado State University, Fort Collins *
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121
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Geology
Date
Dec 6, 2023
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docx
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Uploaded by CorporalLeopard2596
GEOL 121
Name Alexi Lindsay
Lab Section 16
Rocks Lab 3 – Rocks of Colorado and Geologic Maps
Learning Objectives:
1.
Describe, Identify, and Interpret Rocks from Colorado
2.
Find information about the geology of a region from a geologic map
In this week’s lab, you will continue to practice your skills at describing and identifying rocks, this
time using rock samples from the Colorado Front Range. All of the rocks that you will see in lab
this week are rocks that you can see when you are out exploring around Fort Collins and in the
foothills. You will also use a geologic map to gain more detailed information about the rocks of
the Front Range.
Part 1: Rocks of the Colorado Front Range
For each unknown rock sample, you should provide:
1)
A detailed description. Your description should be detailed enough that someone
reading your description could easily pick out which rock you are talking about.
Your description should include information such as the rock’s color, texture, grain
size, minerals present, layering, fossils present, variability, abnormalities, etc.
2)
Whether the rock is igneous, sedimentary or metamorphic, and how you know.
3)
An identification of the rock.
4)
A hypothesis of how the rock formed and the evidence supporting your hypothesis.
Rubric for rock descriptions:
0.5 pt.
0.25 pt.
0 pt.
Descriptions contain enough detail that
someone reading the description could
picture the rock in their mind. Features such
as color, shape, texture, irregularities,
patterns, layering, grain size and shape,
minerals present, etc. are described when
appropriate.
Descriptions are given but lack
adequate detail to fully under-
stand what is being seen.
No response given.
Rocks Lab 3
GEOL 121
Sample #
Rock Description
Rock Type (ign, sed, or
meta)
How do you know?
Rock ID
Formation Hypothesis
And Reasoning
Sample 1
Posted up with black dots, layered
with white and pink. Sharp edges
chiseled structure
It’s an igneous rock.
I know it’s an igneous rock
from the lack of grain
Granite
From volcanoes
Sample 2
Flatter structure, layered well, grey
with a hint of brown
It’s a sedimentary rock.
It fizzed when I enhanced the
liquid upon the rock
Limestone Shale
Reaction to Fizz
Sample 3
Pebbles and sand scattered around
the rock, light tannish color
It’s a sedimentary rock.
Clear pieces of sand on the
rock
Sandstone
Grains of sand we’re
compacted/cemented
together
2
Rocks Lab 3
GEOL 121
Sample #
Rock Description
Rock Type (ign, sed, or
meta)
How do you know?
Rock ID
Formation Hypothesis
and Reasoning
Sample 4
Black shiny crystals displayed all
around the rock.
A Metamorphic rock
I know from the crystals
Schist
Formation from the rock is
the heat and pressure to
then it being formed
Sample 5
Broken up into dozens of pieces but
colored grey with a soft layer
It’s a sedimentary rock.
I know it from the scratches
upon the rock, it’s light on the
nails
Shale
Formation from the
weather being cycled
around impacting the rock
3
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Rocks Lab 3
GEOL 121
Part 2: Geologic Maps
Take a few minutes and examine the map that has been provided.
1) What is this map showing you? What spatial area is this map showing? What do the colors
represent?
The map shows me Horse tooth Reservoir on a quadrangle scale, the area that it’s showing is the
reservoir itself and the mountain hills around it. The colors represent correlation of map units.
2) In what area of the map do you generally find igneous and metamorphic rocks? In what area
of the map do you generally find sedimentary rocks?
Igneous and sedimentary rocks can be found near to bodies of waters, metamorphic can be found
in higher elevations, another find is that sedimentary rocks can be found in lower elevations.
3) Find the rock formation labeled Xbc on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for Xbc?
Xbc on the map is Boulder creek granodiorite. 17,000 +40 ma and the composition
of the formation is medium grained.
4) Find the rock formation labeled Xqs on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for Xqs?
The name is Quartzofeldsphactic mica schist contains the bed of granule and is 17,10 MA
4
Rocks Lab 3
GEOL 121
5) Find the rock formation labeled PPf on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for PPf?
Fountain formation is a schist rock with siltstone and shale.
6)
Find the rock formation labeled Kn/Kns on the map and in the legend.
What is the name, age,
and composition of the formation? Which of the rocks that you previously described best
matches the description for Kns?
The name is smoky hill shale member and it has very fizzle calcareous shale.
7) Find the rock formation labeled Kpl on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for Kpl?
Its name is Pierre Shale, dark olive grey shale with sandy shale.
8) Find Horsetooth Reservoir on the map.
a. Which formations form the east and west edges of Horse tooth Reservoir? What is their
composition?
The formations that form from the east to west edges of Horse tooth are Pierre shale and boulder
creek granodiorite, the composition being shale, grained, and dark olive
5
Rocks Lab 3
GEOL 121
b. Which formations are underneath Horse tooth Reservoir? What is their composition?
The formation that is underneath Horse tooth Reservoir is Lykins formation being siltstone
waterproof.
9) Why do you think the reservoir was placed where it was?
The reservoir was placed where it was due to the many influence of rocks scattered along the
region.
10) What are one or two other potential ways that geologic maps such as this one could be used
by non-geologists to inform their decisions or planning?
Geologic maps such as this one could be used by non-geologist to inform their decision as how
to go upon building recreational areas or housing.
6
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