Getting to GZ:
Park at the Cascade Falls Regional Park parking lot; please note the hours from the website and comply with them.
From the parking lot, follow the gravel road uphill until you see the distinct path (above/past the waterfall observation decks and suspension bridge) heading towards the creek.
Follow the path until you reach a set of ropes to guide you down to the creek level.
Follow the trail until you are taken out onto the creek bed.
Carefully follow the creekbed to GZ, which is featured in the picture below.
Geology of the Area:
As you start at the Cascade Falls you’ll notice an abundance of the speckled granodiorite rocks, particularly filling the creek bed above the falls. These rocks are generally fairly well rounded as they’ve been “tumbled” and polished by weathering and erosion as they have been moved down the creek bed from where they first emerged from the earth eons ago, forming the surrounding mountains.
The granodiorite is an igneous rock with a dense “salt and pepper” appearance very common in this geological region we are in - the Coast Belt.
Like most igneous rock, it was formed by molten rock pushing up from under the earth, and once exposed, broken into different sized pieces by various forces of nature and geology. As this molten rock pushed its way upward, it encountered other minerals and rocks that became trapped inside of it, creating the xenoliths we can find today.
Below is an example of granodiorite from the Cascade Creek region with zenoliths embedded. Note, this image does not provide you the answers to the logging tasks.
What is a Xenolith:
“A xenolith is a piece of rock trapped in another type of rock.
Most of the time, a xenolith is a rock embedded in magma while the magma was cooling. Magma is the molten rock beneath the Earth's crust that emerges as lava during a volcanic eruption. The rock that forms from cooled magma is called igneous rock. Xenoliths are different types of rock embedded in igneous rock.
Xenoliths are torn from deep cracks, or pipes, in the Earth's surface. Magma rises to the Earth's surface through these pipes between the Earth's crust and mantle. As the molten material rises, it tears off bits and pieces of the magma pipe in which it is traveling. These bits and pieces, trapped in the magma but not melting into it, become xenoliths. Crystals that are torn from the sides of magma pipes are called xenocrysts.
As magma erupts or flows from the Earth's surface, it is cooled by exposure to air or water. Lava cools fairly quickly, and various types of igneous rocks are formed. Xenoliths are usually visible. They have a different color and density than the surrounding igneous rock. Xenoliths can be as small as a grain of sand or as large as a football, and as long as several meters.”
Logging Tasks:
Locate the Saddle Rock - it is a large boulder with a relatively flat triangular surface, adjacent to the creek. On the “up-creek” end of the boulder, there are some xenoliths.
- How many xenoliths are readily identifiable on this end of the boulder?
- What is the average size of these xenoliths?
Some of the xenoliths have an unusual colouration on and around them.
- What is that colour?
- Why do you think that colour is present?
- What does this possibly tell us about the mineral content of the rock that the magma which created the boulder encountered during its ascent?
Citations:
Definition of Xenolith taken from National Geographic
From https://www.nationalgeographic.org/encyclopedia/xenolith/