Walking Field Trip From MPC to Del Monte Beach
Logistics: During this lab session we will walk from MPC to Del
Monte Beach, with many stops along the way to see and discuss
evidence for the ocean’s role in shaping our landscape along the
shores of Monterey Bay. Please participate in the discussion and
answer the questions at each of the stops. Please wear walking
shoes and clothes appropriate for spending a couple of hours
outside. If you somehow miss the beginning of lab, go to the
following places to find us or make up the lab.
Observations: the
Key to Scientific
Discovery
Observing our natural
surroundings is the first
step in the Scientific
Method. It allows us to
gather critical
information that will
lead to ask questions
and explain the origin
of the rocks,
landscapes, and
processes around us.
Stop 1: The rock sculpture in the MPC Library courtyard.
Observe the rock, both close up and from a few feet away. List
your observations in the table. What do you see? What colors do
you see? What shapes, or structures do you see? Can you see
individual grains? Are they all the same? What color and size are they?
Observations from a few feet away
Observations close up
Hexagonal and columnar in shape.
Dark grey to black in color with some rustcolored stains on some surfaces.
Feels rough, like fine grained sandpaper.
Can barely distinguish individual grains.
Grains have a crystalline, or interlocked
texture.
Answer the following questions during the conversation with your instructor.
a. What kind of rock is this?
Basalt, a kind of volcanic rock.
b. To which of the three major rock types does this rock
belong?
Igneous, those that cool from magma or lava.
c. What were the key observations that led to this
interpretation?
The fine-grained crystalline nature of the rock
d. Where does this kind of rock most commonly occur
on Earth?
On the ocean floor, and on certain kinds of volcanoes,
like Hawaii.
e. What is special about the “shape” of this particular
rock? How did it form?
It represents contraction as the lava cooled and
solidified. They are similar to mud cracks on a dry lake
bed. In general, solids have higher density than liquids, and cold material has higher
density than warm material, so as the lava cools, solidifies, and cools some more, the
rock contracts; the cracks are the result of the rock cooling and decreasing in volume.
Stop 2: Monterey Formation, in back of the Monterey Art Museum at La Miranda
a. These rocks belong to the Monterey Formation. Observe them from both close up and
from a few feet away. What shapes, or structures do you see? Can you see individual
grains? Are they all the same? What color are they? How big are they?
Observations from a few feet away
Observations close up
The rock is layered.
Cannot see individual grains.
The color is light beige to reddish brown
Brittle; breaks easily.
on some surfaces.
The rock has vertical cracks as well as the
more horizontal layering.
Answer the following questions during the discussion with your instructor.
a. To which of the three major rock types does this rock belong?
Sedimentary
b. What was the key observation that led to this interpretation?
The layered nature of the rock.
c. What is a “depositional setting”?
The kind of location where the sediments that eventually turned into rock, were
deposited, or settled to the bottom of the water body or were deposited on the ground.
Examples include, lakes, rivers, sand dunes, beaches, lagoons, deep ocean, coral reefs,
etc…
d. What is the depositional setting of this rock, belonging to the Monterey Formation?
Deep ocean
e. What is the evidence that we can see (or not see) in the rock that supports our
depositional-setting interpretation?
Very fine grained…therefore a very low energy depositional environment.
The presence of diatom fossils, microscopic organisms that we cannot see with our naked
eye, indicates a deep-water setting far from shore. We could see the diatoms if we had a
scanning electron microscope.
f. What are two hypotheses of how the Monterey formation came to crop out here today?
Either sea level was a lot higher in the past and has since receded, or the rocks were
moved by tectonic forces and lifted up above sea level.
g. Which of these two hypotheses is more likely? Why?
The second one: the rocks were probably moved here by tectonic forces. The reason is
that we are currently at a sea-level high. We know this from considering the effects of ice
ages on sea level in the geologic past. An ice age sequesters water on land as ice, thus
causing sea level to drop.
e. Have you ever seen these rocks anywhere else in the Monterey Bay Area? If so,
where?
They occur in many places along the central coast, including Jack’s Peak and Carmel
Valley among many others.
Stop 3: The “Rock Sculpture” on the shores of El Estero. (El Estero is the body of
water that stretches from Fremont St to Del Monte Avenue.)
a. Observe the rock, both up close and from a few feet away. What do you see? What
colors do you see? What shapes, or structures do you see? Can you see individual grains?
Are they all the same? What color are they? How big are they?
Observations from a few feet away
Observations close up
Rock contains pieces of dark and light
Large grain size
material
Can see individual crystals
Can see sunlight reflecting off many of the Can see different kinds of crystals
grains.
The crystals have an interlocking texture.
Answer the following questions during the discussion with your instructor.
a. To which of the three major rock types does this rock belong?
Igneous
b. What was the key observation that led to this interpretation?
Interlocking crystals that are interpreted to have formed from a cooling magma.
c. Where were these rocks formed?
Deep within the crust.
d. What evidence can you see in the rocks that supports this interpretation.
The large grain size of the crystals; the rock must have formed somewhere warm, where
the magma body cooled slowly, allowing large crystals to form.
Stop 4: The shores of El Estero
a. Why might this little valley and little lake be here in the first place?
It looks like it is in a small valley. Erosion may have played a role.
b. What role does sea level change play in the explanation?
We’re at sea level. In order to get the water to flow to cause erosion, sea level must have
been lower at some time in the past. In the geologic past, an ice age may have caused the
sea level to be lower. During this time, a river may have flowed past here on its way to
the coast. More recently, the climate warmed, causing the glaciers to melt, which in turn
caused the sea level to rise and flood the mouth of the river. Elkhorn Slough is another
good example of this. See the images on the next page.
The next page shows maps of Lake El Estero and Elkhorn Slough.
Lake El Estero (left) and Elkhorn Slough (right), two
examples of river mouths that were flooded with seawater since the last ice age.
Stop 5: On the way down Camino El Estero to Del Monte Beach
a. What kinds of rocks do we see on our way?
More Monterey Formation on the bridge, and metamorphic rock on the traffic island
where we crossed Del Monte Blvd on the way to Del Monte Beach.
b. How are they being used?
As building stones.
Stop 6: Del Monte Beach.
a. Look closely at the sand. Describe what it is composed of.
Light and dark grains. The light grains are the minerals quartz and feldspar; the dark
grains are the minerals amphibole and magnetite.
b. Where does all this sand come from, anyway?
Rivers and eroded sea cliffs. It does not “come from the ocean”.
c. What’s the main process by which sand gets transported down the beach?
Longshore drift. Ocean waves impact the beach at a small angle, pushing the sand up
onto the beach and then pulling to back down the beach. The net direction of travel is
along the beach.
d. Which major landmarks can we see from the beach? (If it’s a clear day we’ll be able to
see quite a few.)
On a clear day we can see Ben Lomond Mt near Santa Cruz, Loma Prieta near the site of
the 1989 earthquake, the stacks at Moss Landing, and Fremont Peak.
e. If we could walk from here to Santa Cruz along the seafloor, what major feature would
we have to cross along the way?
The Monterey Canyon, a canyon as deep as the Grand Canyon in places.