Boulder Park facts for kids
Boulder Park is a special place in Douglas County, Washington, known as a National Natural Landmark. It's famous for showing us what the land looked like after the last great Ice Age. Along with other nearby spots like McNeil Canyon Haystack Rocks and Sims Corner Eskers and Kames, Boulder Park has amazing examples of landforms created by melting ice.
You can see many huge rocks here called glacial erratics and "haystack rocks." These rocks are found near and on something called the Withrow Moraine, which is like a big pile of dirt and rocks left by a giant ice river called the Okanogan ice lobe.
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What is Boulder Park?
Boulder Park is located on the Waterville Plateau, which is a flat, high area in central Washington state. Imagine a giant, shallow bowl that gently slopes north – that's kind of what this area looks like. The Waterville Plateau stretches from the Columbia River all the way to the Grand Coulee.
This plateau is made of old basalt rock from the Columbia River. On top of this rock, there's a scattered layer of glacial deposits, which are bits of rock and dirt left by glaciers about 14,000 to 20,000 years ago.
How Glaciers Shaped the Land
Boulder Park is about 6 kilometers (3.7 miles) northeast and 17 kilometers (10.5 miles) north of the Withrow Moraine. This moraine shows us where the Okanogan ice lobe, a huge part of the Cordilleran Ice Sheet, stopped advancing about 17,000 years ago.
The area around Boulder Park is covered with a mix of gravel, sand, and clay, all left by the glaciers. These glacial deposits cover an old river channel called Moses Coulee. This channel was carved out by massive floods even before the last Ice Age. At its biggest, the Okanogan ice lobe was about 300 meters (984 feet) thick and 40 kilometers (25 miles) wide! It was so big it blocked most of the Columbia River Valley, creating a huge lake called Glacial Lake Columbia.
The Giant Boulders
The park is named after the huge rocks you can find there. These are the glacial erratics and "haystack rocks." They were carried here by the Okanogan ice lobe.
- Glacial Erratics: These are rocks like granite and gneiss that were picked up by the glacier from far away and dropped here. They don't match the local rock.
- Haystack Rocks: These are huge pieces of basalt that were ripped right out of the local ground by the glacier. Even though they are huge, they are made of the same rock as the area around them. They get their name because, from a distance, they can look like black haystacks. Some, like Yeager Rock, are as big as houses!
These giant boulders are important clues. They show us how powerful glaciers are at moving things, and they help scientists figure out where the Okanogan ice lobe moved and where it finally stopped during the last Ice Age.
The Rocks Underneath
Underneath all the glacial deposits, you'll find much older rock called the Priest Rapids Member of the Wanapum Basalt. This rock formed during the middle Miocene period, which was millions of years ago. It's a grayish-black rock made of fine to coarse grains. It's part of the larger Columbia River Basalt Group.
The Columbia River Basalt Group is a huge area of lava flows that covers parts of Washington, Oregon, and Idaho. It's one of the largest areas of volcanic rock in the world! It covers about 163,700 square kilometers (63,000 square miles) and has an estimated volume of 174,300 cubic kilometers (41,800 cubic miles) of basalt lava. Most of these eruptions happened very quickly between 17 and 14 million years ago. Some smaller eruptions continued until about 6 million years ago.
Images for kids
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Mixed erratics located near Sims Corner. The nearest is basalt, while the ones behind it are granite.
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A kame (a hill of sand and gravel) among the glacial drift on the terminal moraine.
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The terminal moraine (Withrow Moraine) of the Okanogan Lobe.
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Many erratics on the terminal moraine of the Okanogan Lobe, with the Cascade mountains in the background.
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More erratics on the terminal moraine of the Okanogan Lobe.
