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Please respect the area - do not collect rocks, and leave the landscape as you found it. This EarthCache is here to inspire curiosity and appreciation for our planet’s story.
LOGGING REQUIREMENTS: To claim this EarthCache 
, you must first visit the posted coordinates and then Send Answers via the geocaching.com Message Center to the following questions based on your observations and the information provided in the short Earthcache Lesson below:
- Describe the rocks around the pond. What color and texture do they have? Based on your observations, what kind of rock might you be seeing? (e.g. oliphite, glacial debris)
- Observation: Do you see evidence of quarrying activity? Describe a human-made vs. natural feature
- Optional: Post a photo of your visit (without revealing answers)
Welcome to Quarry Pond!
EARTHCACHE LESSON: Quarry Pond isn’t just a peaceful campsite tucked into the forest—it’s a living museum of Earth’s dynamic history. Beneath your feet lies an ancient seafloor, shaped by tectonic forces, gouged by glaciers, and later transformed by human hands. This EarthCache invites you to explore the area and uncover clues to its remarkable past.
150 million years ago: Fidalgo Ophiolite - Walking on the Ocean Floor
The story of Quarry Pond starts deep beneath the ocean—literally. The bedrock in this area belongs to a unique geological feature known as the Fidalgo Ophiolite, a rare and fascinating remnant of ancient oceanic crust and upper mantle that now forms part of the land.
An ophiolite is a geologic structure that represents a slice of the ocean floor that has been uplifted and emplaced onto continental crust—a process that typically happens at convergent plate boundaries, where oceanic plates are subducted beneath continents. Most oceanic crust is recycled back into the Earth’s mantle, but in rare cases like this one, pieces are scraped off and preserved on land. That’s what makes the Fidalgo Ophiolite scientifically significant.
This ophiolite formed approximately 150 million years ago during the late Jurassic period as volcanic activity
created new crust at a mid-ocean ridge. The rocks here include:
- Pillow basalts – These rounded, bulbous lava formations occur when molten basalt erupts under water, cooling quickly into characteristic “pillow” shapes. You might see these along outcrops near the pond and on nearby coastal trails.
- Chert – A hard, silica-rich rock made of microscopic marine plankton that settled on the ocean floor. Often reddish or gray, chert forms thin, brittle layers and may be found interbedded with other rocks in the area.
- Graywacke – A gritty, dark sandstone composed of volcanic fragments and clay, typically deposited in deep-sea environments by submarine landslides.
- Serpentinite and gabbro – Deeper sections of ophiolites sometimes preserve rocks from the Earth's upper mantle or lower crust, though these are harder to identify in the field without a trained eye.
These rocks were later metamorphosed and deformed due to intense pressure and heat during tectonic collisions, as the oceanic plate collided with and was shoved beneath the edge of the North American continent. This accretionary process added slices of ocean floor—called terranes—to the growing North American landmass. The Fidalgo Ophiolite is one such terrane, and it’s a key piece of the geologic puzzle that helped form the Pacific Northwest.
The ophiolite at Quarry Pond is part of a broader pattern in the Pacific Northwest, where several terranes of differing origins have been stitched together through tectonic processes. Studying these rocks helps geologists better understand how continents grow over time and how oceanic and continental crust interact.
Even if you're not a professional geologist, standing here at Quarry Pond, you’re experiencing something rare: walking on ancient ocean floor that has been through an epic journey—formed at a mid-ocean ridge, buried beneath ocean sediments, crumpled by tectonic forces, and finally lifted skyward to become part of a state park trail. That’s what makes the Fidalgo Ophiolite so exciting.
Observation: As you explore, look for signs of layering, folding, or pillow shapes in exposed rock. Can you find any evidence of Quarry Pond’s oceanic origins?
~1-2 million years ago: Glacial Sculpting
Fast-forward to the Pleistocene Epoch (~2 million to 12,000 years ago): Massive continental glaciers advanced across the region. These slow-moving ice sheets scraped and scoured the land, leaving behind features like:
- Glacial striations – Grooves carved into rock by debris-laden ice.
- Rounded outcrops – Smoothed and polished by ice movement. Nearby Goose Rock (N 48° 24.069′ W 122° 38.354′; Terrain 4) offers some of the best examples of glacial shaping in the park.
100 years ago: Human Impact
In the early 1900s, this area was transformed again—this time by people. The site became a working rock quarry, operated using convict labor starting around 1909. Prisoners crushed stone here to help build roads and local infrastructure. Remnants of this time include:
- The quarry’s steep rock walls and flat floor
- Historical accounts of a rock crusher and transport bridge
When the quarry was abandoned, groundwater and rain naturally filled the pit, creating the tranquil Quarry Pond you see today.
Observation: Look for sharp, vertical cuts in the rock and unnatural slopes—these features contrast with the more rounded forms left by glacial activity.
Sources:
https://www.friendsofwhidbeystateparks.org/deception-pass-geology
https://nwgeology.wordpress.com/the-fieldtrips/fidalgo-ophiolite-part-2/
https://deceptionpassfoundation.org/news/rock-quarry-and-convict-camp/
https://parks.wa.gov/about/news-center/field-guide-blog/deception-pass-state-park-history
https://www.researchgate.net/publication/237173457_Stratigraphy_depositional_setting_and_tectonic_significance_of_the_clastic_cover_to_the_Fidalgo_Ophiolite_San_Juan_Islands_Washington
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1. This geocache has an approved Permit to be placed at this location on property managed by the Washington State Parks and Recreation Commission. Visitors are responsible for acquainting themselves with policies and rules pertaining to State Parks areas.
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