Glacial erratic boulders of the Puget Sound region facts for kids
Many glacial erratic boulders are huge rocks that were carried by ancient glaciers. You can find lots of them in the Puget Sound region of Washington State. Some are as far south as the Yelm area, which is where the huge glacier stopped.
These amazing rocks are leftovers from the Pleistocene ice age. During that time, a massive glacier covered the Puget Sound area. It carved out many of the landforms we see today, including Puget Sound itself! A geologist named Nick Zentner from Central Washington University says these "Canadian rocks" are spread all over the Puget lowland. You can find them from the Olympic Peninsula all the way to the Cascade Mountains.
Some erratics are found high up, about 1,300 to 1,600 feet (396 to 488 meters) high, near Enumclaw. The soil in Seattle, Washington's biggest city, is mostly made of material left behind by glaciers. Many of Seattle's famous hills, like Beacon Hill and Queen Anne Hill, are actually "drumlins." Drumlins are small, oval-shaped hills formed by glaciers. While very large boulders (over 3 meters wide) are rare, you can still find them.
Famous Glacial Erratics in Puget Sound
Here are some of the biggest or most interesting glacial erratics you can find in the Puget Sound area.
| Name and description | Height | County | Image |
|---|---|---|---|
| Airport Boulder is at Martha Lake Airport Park in Martha Lake. People say it's one of the biggest erratics in the urban areas of King, Snohomish, and Pierce counties. It's about 20 feet (6 meters) long and twice as tall as a person! This rock is made of greenstone and is popular for rock climbing.
47°51′53.7″N 122°14′10.7″W / 47.864917°N 122.236306°W |
12 feet (3.7 m) | Snohomish |  |
| Arroyo Park erratic is in Arroyo Park in Bellingham. It stands about 10 feet (3 meters) tall and is 17 by 23 feet (5.2 by 7 meters) wide. It's mostly made of diorite rock.
48°41′54″N 122°28′45″W / 48.6983°N 122.4793°W |
10 feet (3.0 m) | Whatcom | |
| Big Rock is an 8-foot (2.4-meter) tall erratic in Duvall. A road, a park, and many businesses in Duvall are named after it. This rock, along with two giant redwood trees next to it, is a local landmark. The rock is in what might be the smallest park in King County!
47°43.542′N 121°59.189′W / 47.725700°N 121.986483°W |
8 feet (2.4 m) | King |  |
| Big Rock in Coupeville was once called the Rock of Ages. This greenstone erratic is a famous landmark on Main Street.
48°12′38″N 122°41′14″W / 48.21056°N 122.68722°W |
30 feet (9.1 m) | Island | |
| Dabob Bay erratic is a large conglomerate rock on the shore of Dabob Bay. It might have come from the Chuckanut Formation in Whatcom County, which is 80 miles (129 km) away!
47°48′N 122°48′W / 47.8°N 122.8°W |
Jefferson | ||
| Discovery Park beach erratics are four or more large rocks found on the beach below Discovery Park. The biggest one is 15.33 feet (4.67 meters) high and 69.5 feet (21.2 meters) around.
47°40.124′N 122°25.210′W / 47.668733°N 122.420167°W |
15.33 feet (4.67 m) | King |  |
| Fort Townsend State Park erratics are two erratics in Fort Townsend State Park. One is granite, likely from British Columbia. The other is basalt, possibly from B.C. or the Olympic Peninsula.
48°04′24″N 122°47′22″W / 48.07333°N 122.78944°W |
Jefferson | ||
| Four Mile Rock is a round granite erratic, about 20 feet (6 meters) across. It sits in the water near Seattle's Magnolia Bluff. There's even a light on it to help boats navigate! Native Americans had special names for this rock and a legend about it.
47°38′20″N 122°24′48″W / 47.63889°N 122.41333°W |
15 feet (4.6 m) | King |  |
| Frog Rock is a well-known landmark on Bainbridge Island.
47°41′46″N 122°31′24″W / 47.69612°N 122.52347°W |
7.33 feet (2.23 m) | Kitsap |  |
| Lake Lawrence erratic is near Lake Lawrence in Thurston County. This rock is one of the southernmost erratics left by the Vashon Glacier.
46°51′54″N 122°34′45″W / 46.86507°N 122.57904°W |
15 feet (4.6 m) | Thurston |  |
| Lake Stevens Monster is near Lake Stevens. It's huge, measuring 34 by 78 feet (10 by 24 meters) and 210 feet (64 meters) around! As of 2011, it was the largest known erratic in Washington State. It might even be the largest in the United States!
47°59.816′N 122°6.954′W / 47.996933°N 122.115900°W |
34 feet (10 m) | Snohomish |  |
| Lone Rock is the name of a small community. This huge rock is located on the Hood Canal tidal flat, about 400 feet (122 meters) from shore. It's at least 50 feet (15 meters) across!
47°39′47″N 122°46′12″W / 47.66297°N 122.769916°W |
50 feet (15 m) | Kitsap |  |
| Oyster Bay erratic is on the shore of Oyster Bay in Thurston County.
47°6′15.5″N 123°4′3.0″W / 47.104306°N 123.067500°W |
12 feet (3.7 m) | Thurston |  |
| The Skystone in Bonney Lake is an andesite erratic. It may have been important to the Puyallup tribe of Native Americans for watching the sky. One expert called it "the new world Stonehenge." It is 4.5 by 12 feet (1.4 by 3.7 meters).
47°09′14″N 122°11′41″W / 47.153807°N 122.194685°W |
4.5 feet (1.4 m) | Pierce |  |
| Waterman Rock is found in Saratoga Woods Preserve near Langley.
48°03′38″N 122°27′47″W / 48.06056°N 122.46306°W |
38 feet (12 m) | Island |  |
| Wedgwood Rock is a famous erratic near the Wedgwood neighborhood in Seattle, Washington. It is 80 feet (24 meters) around and 19 feet (5.8 meters) tall. Since 1970, it has been against the law to climb this rock.
47°40′51″N 122°17′50″W / 47.68084°N 122.2973°W |
26 feet (8 m) | King |  |
| White Rock is a white rock in the water at the head of Hood Canal. It's white because of bird droppings!
47°53.593′N 122°38.579′W / 47.893217°N 122.642983°W |
24 feet (7.3 m) | Jefferson |
