The Big Obsidian Flow Trail Newberry National Volcanic Monument, Oregon 

The Big Obsidian Flow is a mountain of volcanic glass. It erupted 1300 years ago and is considered "young" in geologic terms. It is also the largest obsidian flow in North America and Native Americans used it to make high-quality tools that were traded throughout the West. This 3/4-mile interpretive trail climbs up onto the flow and loops around to several scenic viewpoints. It took Dick more than two years to complete the layout and design. Walking and surveying was extremely difficult since the glass shredded everything that touched it, but the result is a trail that is one of the highlights of the National Monument.