Mount Rainier National Park, Washington. 235,625.00 acres. Mt. Rainier, an active volcano, is the most prominent peak in the Cascades and it is covered by 26 named glaciers. The mountain is popular for climbing and more than half the park is covered by subalpine and alpine forests. Paradise, on the south slope is one of the snowiest places in the world and the Longmere visitors center is the start of the Wonderland Trail, which encircles the mountain.