Oregon Magazine

Simon Says:
Volcanic Glass is Sharper Than Steel
by Simon Skiles

                Seventy miles east and 24 miles south of Bend, OR are two of the state’s largest deposits of obsidian: Glass Buttes (photo below on the left) and Newberry Caldera. Both are open to the public and both are quite amazing.


               Obsidian is a volcanic glass that forms when lava cools rapidly, preventing the formation of crystals. It is comprised of silicon dioxide (known as sand or quartz) and iron or magnesium. The color of obsidian depends on the quantities of these elements. Iron gives the glass its black color.

                Native Americans in the Northwest used obsidian to make arrowheads and spears. Today it is used in the manufacture of scalpels. Obsidian edges are much finer and smoother than steel scalpels and result in less scarring when an incision heals after surgery. The other most common use for obsidian today is jewelry.

                 Glass Buttes are a small mountain range in Central Oregon that contains large quantities of obsidian. The area formed approximately 5 million years ago when volcanic activity was located in that region, instead of where it is today in the Cascades. These mountains are mostly rounded formations due to a prolonged period of erosion. Obsidian pieces are found scattered on the ground (photo left) all around the base of the area, not just on the peak itself.

                Newberry Caldera is a shield volcano that is considered active in geologic terms. Its most recent eruption was approximately 1300 years ago. This produced the Big Obsidian Flow, which covers 700 acres and is dozens of feet tall. This flow is so recent that only a few small trees have had time to establish themselves among the rocks. Massive pieces of obsidian are located here. (photo just below)

                My trip to these two locations started with the Glass Buttes using highway 20 to arrive at the northern edge. The dirt road I wanted to explore (it leads into the heart of the buttes) was fenced off. I had to settle for a different route that was open and crossed alternating squares of private and BLM (Bureau of Land Management) land. I found it unnecessary to get close to the buttes; obsidian lay everywhere on the ground some distance from the peak. I managed to find a couple of decent pieces of obsidian larger than my fist.

                Newberry Caldera was much easier to access and the Big Obsidian Flow was easy to find. I hiked a trail into the flow and found signs along the path, one of which taught me about the use of obsidian for scalpels. Rock collecting is not allowed here and so I only took photos. At 6500 feet, even in late June, the weather was chilly and there were still patches of snow on the ground.

                Oregon has many fascinating geologic formations and these two locations do not even scratch the surface. However, for large collections of obsidian in one location, there are few examples better than Glass Buttes and Newberry Caldera.


Glass Buttes are on BLM land and are open to the public. There are three dirt roads leading south from highway 20. The road farthest east is called Obsidian Road and has been fenced off the two times I have been there. Why? Even as a BLM employee, I have no answer. The next road has no name and is only accessible by four-wheel drive. The third westerly road is easily accessible by car and is a mostly smooth path to the west face of the buttes. This crosses both public and private land, so be sure to know where you are before you collect samples.

Newberry Caldera is accessible by paved road from the west off highway 97. There is a $5 fee to enter the national monument and Big Obsidian Flow is a couple of miles inside the monument boundary. The place is popular and you will likely encounter other people. Again, rock collecting is not allowed here.


© 2009 Simon Skiles