Glacial erratic boulders of King County, Washington facts for kids
Have you ever seen a giant rock sitting all by itself in a field or park, far from any mountains? These huge rocks are called glacial erratic boulders. They are special rocks that were moved into King County, Washington by powerful glaciers during past ice ages. Imagine a giant bulldozer made of ice pushing these rocks along!
During the last big Pleistocene ice age, huge glaciers shaped the land around Puget Sound. They created many of the features we see today, like Puget Sound itself. The glacial erratics are like clues left behind from that icy time. A geologist named Nick Zentner from Central Washington University says that "Canadian rocks [are] strewn all over the Puget lowland." This means rocks from Canada were carried all the way to Washington! You can find these erratics in places like Enumclaw, sometimes as high as 1,300 to 1,600 feet up. The soil in Seattle, the biggest city in King County, is mostly made of material left by glaciers. Many of Seattle's famous hills, like Beacon Hill and Capitol Hill, are actually "drumlins," which are long, oval-shaped hills formed by glaciers. While most rocks left by glaciers are small, some boulders bigger than 10 feet across can be found, as you'll see below.
Cool Glacial Erratic Boulders in King County
Here are some of the most interesting glacial erratic boulders you can find in King County:
| Name and description | Height | Image |
|---|---|---|
| Beaver Lake Preserve Erratic
These huge rocks are found in and around a protected area in Sammamish. Some of them weigh as much as 100 tons! Beaver Lake itself is a "kettle lake," also formed by glaciers. In the 1950s, people reported seeing otters resting on the largest erratic at the north end of Beaver Lake. 47°35′31.1″N 121°59′27.0″W / 47.591972°N 121.990833°W |
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| Big Rock (Duvall)
This is an 8-foot-tall glacial erratic in the city of Duvall. It's so famous that a road, a park, and several businesses are named after it! The rock and two giant redwood trees next to it are a local landmark. The rock sits in what might be the smallest park in King County, just 20 by 70 feet. 47°43.542′N 121°59.189′W / 47.725700°N 121.986483°W |
8 feet (2.4 m) |  |
| Big Rock Park Erratic (Sammamish)
This erratic is in a park with the same name in Sammamish. People even thought about calling the park "Bigger Rock Park" to make sure it wasn't confused with the one in Duvall! 47°36′00″N 122°02′49″W / 47.600°N 122.0469°W |
8 feet (2.4 m) |  |
| Cascadia College Erratic
This rock was almost destroyed during construction! Students from Cascadia College who were studying environmental politics held a "sit-in" to save it. Several students sat on the rock to protect it. The rock was about 6.5 feet across before it was cut down to two-thirds of its original size. 47°45′38″N 122°11′20″W / 47.76059°N 122.18886°W |
3 feet (0.91 m) |  |
| Des Moines Beach Erratic
You can find this rock near Des Moines Beach Park in Des Moines. It measures about 8 feet long, 6 feet wide, and 4.5 feet high. 8 by 6 by 4.5 feet (2.4 m × 1.8 m × 1.4 m) 47°24.250′N 122°19.848′W / 47.404167°N 122.330800°W |
4.5 feet (1.4 m) |  |
| Discovery Park Beach Erratics
There are at least four large erratics on the beach below Discovery Park in Seattle. The biggest one is about 15.33 feet high and 69.5 feet around! 47°40.124′N 122°25.210′W / 47.668733°N 122.420167°W |
15.33 feet (4.67 m) |  |
| Fantastic Erratic
This amazing glacial erratic is in Cougar Mountain Regional Wildland Park near Bellevue. It's about the size of a two-car garage and stands 15 feet tall! 47°31′48.9″N 122°4′49.7″W / 47.530250°N 122.080472°W |
15 feet (4.6 m) |  |
| Four Mile Rock
Also known as Fourmile Rock, this round granite erratic is about 20 feet across. It sits in the water near Seattle's Magnolia Bluff and is even marked on nautical charts with a light for boats. Native Americans had special names for this rock, like LE'plEpL. A legend says a hero could throw a giant fishing net over the rock from the beach! 47°38′20″N 122°24′48″W / 47.63889°N 122.41333°W |
15 feet (4.6 m) |  |
| Highline College Erratic
This unnamed erratic at Highline College is made of granite and has cool patterns called "en echelon dikes." It's about 21 by 12 feet and 9 feet high. 47°23′14″N 122°18′06″W / 47.38730°N 122.30173°W |
9 feet (2.7 m) |  |
| Homage Artwork Boulders
These are three groups of "local granite boulders" used in an art project in the Bridle Trails neighborhood of Bellevue. It's interesting because granite bedrock doesn't naturally appear in this part of King County, meaning these rocks were brought here by glaciers! 47°37′57.8″N 122°10′46.3″W / 47.632722°N 122.179528°W (NE 24th) |
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| Leschi Park Erratic
In Seattle's Leschi Park, you'll find this sandstone erratic. It has many fossil shells inside it! Scientists think it might have come from near Mount Baker or from the Harrison Lake area in British Columbia, Canada. It's about 5 feet tall. 47°36′04″N 122°17′20″W / 47.60103°N 122.28897°W |
5 feet (1.5 m) |  |
| Lone Rock
This single, large erratic is located in Tiger Mountain State Forest. It stands about 15 feet high. 47°29.94′N 121°58.17′W / 47.49900°N 121.96950°W |
c. 15 feet (4.6 m) |  |
| Ravenna Park Erratic
In Seattle's Ravenna Park, there's a granodiorite rock about 9 feet tall in Ravenna Creek. A wooden footbridge wraps around it, making it easy to see up close. 47°40′19″N 122°18′25″W / 47.67183°N 122.30689°W |
c. 10 feet (3.0 m) |  |
| Talus Rocks
This is a collection of piled-up erratics in Tiger Mountain State Forest. They form rock caves, sometimes called "Devil's Dens," which are said to be some of the biggest in Washington. The rocks are about 12 feet high. 47°31′07.1″N 121°59′49.2″W / 47.518639°N 121.997000°W |
c. 12 feet (3.7 m) |  |
| Thornton Creek Erratic
You can find this erratic near 17th Ave. NE and NE 104th St. in Seattle's Kingfisher Natural Area. A local group calls the area around this boulder "Erratic Flats." It's about 8 feet tall. 47°42′14″N 122°18′37″W / 47.70389°N 122.31028°W |
c. 8 feet (2.4 m) |  |
| Wedgwood Rock
This famous glacial erratic is near the Wedgwood neighborhood in Seattle, Washington. It's known to geologists as the "Wedgwood Erratic." It's about 80 feet around and 19 feet (or 8 meters) high! Since 1970, it has been against the rules to climb this rock, with a $100 fine if you do. 47°40′51″N 122°17′50″W / 47.68084°N 122.2973°W |
26 feet (8 m) |  |
| Wedgwood Square Park Erratic
This unnamed erratic is located in Wedgwood Square Park. It's about 4 feet tall. 47°41′18″N 122°17′41″W / 47.6882°N 122.2948°W |
c. 4 feet (1.2 m) |  |
