- Wouldn’t it be cool to have a view deep into the Earth? Or should we say it would be hot? Luckily, you don’t need to make a journey to the center of the earth to look at or even touch a piece of Earth’s mantle. Visit the craggy peaks of the Twin Sisters massif and you will see a relatively rare type of mantle rock known as dunite. Hundreds of geologists have studied these rocks in order to untangle their mysteries. Of course, geology is not the only reason to visit the Twin Sisters. In winter, find snow-dotted peaks nestled against a backdrop of forested hills and pastures. In summer, the deep orange to brown shades of the iron-rich ridgeline provide clues about the geologic origins of these mountains. Catch some great mountain sunsets from the valley or hike up the backside of the mountain to the Park Butte lookout for unobstructed views of Mount Baker and Twin Sisters.