I went on a field trip recently to one of my favorite places–Glass Buttes. Obsidian is everywhere you look! It’s like being a kid in a candy store. In fact in one of my previous posts, Glass Butte Dragonglass, I show a picture of some obsidian I have collected displayed in a candy bowl.
Glass Buttes – Rockhounding and habitat
Located about halfway between the towns of Bend and Burns in eastern Oregon, this site is a rockhounder’s paradise. You can dig and crack open obsidian with a rock hammer, but you really don’t need to because it’s all over the surface. The Bureau of Land Management oversees most of this site. Individuals may collect up to 250 pounds of obsidian per year.
Glass Butte, elevation 6,388 ft., and Little Glass Butte, elevation 6,155 ft., tower over the surrounding hills. Sagebrush, rabbitbrush, and bunchgrass cover the landscape. Western juniper and mountain mahogany are interspersed over the land. Sagebrush-dependent species such as Brewer’s sparrows, sagebrush sparrows, and sage thrashers were seen and heard the day we were there. A pair of mountain bluebirds was seen perching high in the juniper trees. We caught glimpses of ferruginous hawks.
Geological history of Glass Buttes
Glass Buttes formed during the Miocene and Pliocene periods, 5-5.8 million years ago. Three layers of lava flows from volcanic domes and vents formed the buttes. The first flow was basalt, the second rhyolitic lava, and the third another layer of basalt. Rhyolite contains a high percentage of silica and it forms much of the substrate. Due to a rapid rate of cooling of magma at Glass Buttes, larger mineral crystals didn’t have time to form. The silica-rich “glass” of obsidian formed as a result of this process.
Here’s an interesting article with more details about the obsidian at Glass Buttes for you geology geeks. Obsidian is Hot Stuff.
This area is in the Brothers Fault Zone of the High Lava Plains physiographic province. The many faults are easily observed in aerial photos and through the use of Light Detection and Ranging (LiDAR) data. A 2011 map of Glass Buttes based on LiDAR can be seen here.
Flint knappers then and now
Obsidian from Glass Buttes has been used in making tools for thousands of years. Native Americans made arrowheads, spear points, and other cutting tools with the glass-like stone. Obsidian from this site has been found throughout western North America.
Modern day flint knappers take advantage of the abundance of obsidian at this site. Some groups meet annually at events such as the Glass Buttes Knap-in to work on their craft. My first photo on this post shows what flint knappers left behind at one of their campsites.
Obsidian from Glass Buttes, Oregon
Types of obsidian at Glass Buttes
There are MANY types of obsidian at Glass Buttes. I will quote Tim Fisher who runs the Oregon Rockhounds Online website. “Need a list of what’s here? OK, here goes: black/mahogany, leopardskin, mahogany, Midnite lace, triple flow, double flow, pumpkin, purple and silver sheen, gold sheen, silver sheen, rainbow, peacock, purple sheen, fire, green, Aurora Borealis rainbow, black, opaque black, opaque banded, gunmetal, and probably many more!” If you want detailed information on where to find the different types, please purchase the Ore Rock On guide from his website. We own it and it contains invaluable info for sites in Oregon, Washington, Idaho and western Montana.
Some rockhounds search for specific types, such as rainbow and fire obsidian, and they can be the most difficult to find.
Exploratory geothermal site
Other land use
We made a couple additional short stops on the field trip. We stopped at an abandoned mercury-bearing cinnabar mine. The site was discovered in 1933 and mined until 1957. Another stop was made at an exploratory geothermal well site. No development is currently taking place but it may happen in the future. Greater sage-grouse live and breed here and that may limit development.
This is a great area to visit but I should remind you of a couple things. Obsidian is SHARP so make sure you have good tires and a spare tire. Four-wheel drive vehicles are recommended for certain areas. There is no water or facilities here. If you visit, be prepared. Access to this site is on an unmarked road near mile marker 77 on Highway 20. Drive south a couple miles to find obsidian. Additional information is available from the organizations listed here.
I have been to this site several times. My recent trip was with Bend Parks and Recreation. I always wish I could stay at Glass Buttes just a little bit longer. It’s a hard place to leave if you love rocks!