Green Brief: The amazing stories rocks can tell

Published 1:30 am Wednesday, February 11, 2026

Have you ever wondered what lies beneath your feet as you walk along Vashon beaches at low tide?

We are fortunate to have an amazingly diverse collection of rocks waiting to be recognized and appreciated. Each beach rock tells a rich story—from its initial formation, often deep within the Earth, to being picked up by the last ice sheet nearly 20,000 years ago and carried here before finally emerging on our beaches as shoreline bluffs erode.

You’ll have another opportunity to learn about Vashon’s remarkable geological history the day after Valentine’s Day. The Vashon Union of Geologists (VUG), in partnership with the King County Library System, invites you to the 5th Antique Rock Show (Love Rocks) on Sunday, February 15, 2026, from 1:00–3:30 pm at the KCLS Vashon Library.

The event is free, registration is not required, and all ages are welcome. Bring your favorite rocks for informal assessment by a panel of geologists, ask questions about the island’s geology, and explore a fascinating display of stones—most collected right here on Vashon beaches.

You can also enter drawings for door prizes or compete for awards such as “Most Spherical” and “Most Heart-Shaped” beach rock.

Vashon’s beach rocks play an important role in shoreline stability and are closely tied to intertidal habitats, influencing algae, invertebrates, and fish nurseries.

Like the island’s ecosystems, the rocks themselves are diverse because they originated from many different landscapes upstream of where the ice sheet once flowed—including British Columbia, the Olympic Peninsula, the North Cascades, and the broader Salish Sea region.

All three major rock groups—igneous, metamorphic, and sedimentary—are represented on Vashon beaches.

Here are a few especially interesting examples. Some of the deepest rocks you might encounter are fragments of the Earth’s upper mantle, known as serpentinized peridotite, torn from the Fidalgo Complex exposed near Washington Park in Anacortes and nearby islands.

Another rare metamorphic rock is nephrite jade, formed when basalt or peridotite is transformed under high pressure and low temperature in subduction zones. These likely originated in British Columbia or the northern Cascades.

Moving to the igneous rock family—stones that were once molten magma—you may find granitic rocks from the Coast Ranges of British Columbia and the Cascades, as well as white-spotted basalt and andesite porphyries with large feldspar crystals.

Also present are ignimbrites and welded ash-flow tuffs, the products of massive volcanic eruptions like the one that formed Crater Lake, Oregon.

The greenish basaltic rocks of the Siletzia terrane formed as a massive, 20-kilometer- thick oceanic plateau far out in the Pacific Ocean about 56 million years ago and were accreted to North America around 50 million years ago.

These rocks include submarine lava breccias and ash beds and owe their green color to metamorphic minerals such as chlorite. Siletzia pillow basalts can be seen today along Hurricane Ridge Road in Olympic National Park.

Among the oldest rocks you might find are pink to brown quartzites of the Belt Supergroup, which began as sands deposited in deserts or shallow seas between roughly 400 million and 1.3 billion years ago. These sediments were later buried, recrystallized, uplifted, and exposed, producing the dense quartzites often crosscut by white quartz veins.

Another silica-rich rock is chert, which occurs in a range of colors—red, gray, black, yellow, and green—and often shows a distinctive network of thin white quartz veins.

Chert formed from the siliceous skeletons of microscopic plankton such as radiolaria and diatoms that lived in ancient oceans more than 150 million years ago. After these organisms died, their remains settled on the seafloor, forming siliceous ooze that was later buried, metamorphosed, uplifted in places like the San Juan Islands, and eventually transported to Vashon by glacial ice.

Sedimentary rocks found on Vashon beaches include conglomerates, sandstones, and mudstones formed in underwater sediment flows known as turbidites on the outer continental shelf more than 20 million years ago. These rocks are now exposed in the Olympic Mountains.

Other metamorphic rocks you may encounter include phyllite, schist, and gneiss, some containing garnet. Garnet crystals liberated from gneiss are relatively hard and dense, allowing them to concentrate in placer deposits on sandy beaches—much likethe famous ruby sands of the Olympic Coast.

Recent king tides and winter storms created ideal conditions for these red sands to accumulate along parts of Vashon’s east shoreline. Samples will be on display at the event, where visitors can also examine them under a microscope.

One of the joys of Vashon’s beaches is that every tidal cycle rearranges many stones, offering a constantly changing palette of ancient materials along our dynamic shorelines.

Living atop an active subduction zone ensures that both the land—and the stories it tells—continue to evolve.

These stories help anchor environmental awareness through a sense of place, deep time, sight, and touch. In many ways, Vashon Island itself is a climate and tectonic artifact: most of its rocks were formed elsewhere and delivered here by ice.

These ancient rocks remind us that our beaches are not static displays but living systems that depend on natural erosion, sediment movement, and restraint in development.

Environmental stewardship here includes understanding these processes and protecting the pathways that allow beaches to renew themselves.

We look forward to hearing more of these stories with you at the 5th Antique Rock Show.

Steve Bergman is a geologist, Zero Waste Vashon board member and Whole Vashon Project advisor.