Where Oregon’s Rainbow Hides in Glass

THE TREASURE OUTSIDE

Some treasures are hidden because someone put them there.

Others have been waiting millions of years for someone to notice.

Along Highway 20 between Bend and Burns, a road turns south into the Oregon high desert toward Glass Buttes. Despite the open, remote country surrounding it, the main access is not difficult to find. Within a few miles, the highway is behind you and the volcanic landscape begins to take over.

Then the glass begins to appear.

Obsidian lies across parts of this country in remarkable variety: deep black, mahogany, red, silver sheen, gold sheen, rainbow and other combinations of color. Glass Buttes is an ancient volcanic complex, and the obsidian found here was formed millions of years ago. Geological studies have identified multiple chemically recognizable obsidian sources throughout the area. (Ambroz, Glascock and Skinner, 2001; Stueber and Skinner, 2015)

That was what brought me here.

I wanted to explore Glass Buttes and see what I could find for myself.

I came home with several pieces of dark volcanic glass. Some were eventually cut and polished, and only then did I begin to see what had been hiding inside.

A piece can appear almost completely black.

Turn it toward the light and suddenly there is color.

Red can move into orange and yellow. Green, blue and violet can appear. Some pieces carry gold, bronze or combinations that seem to shift as the stone moves. Change the angle again and the entire display can disappear back into black.

Round polished piece of black fire obsidian from Glass Buttes, Oregon, with subtle rainbow iridescence appearing in the light. — Not every angle reveals the rainbow. In this piece of polished Glass Buttes obsidian, only a narrow trace of iridescence is visible within the dark glass.

Among the pieces I had carried home was fire obsidian.

And hidden among the enormous amount of obsidian at Glass Buttes, fire obsidian is something much rarer.

The Gemological Institute of America describes fire obsidian as a rare variety of volcanic glass known from a particular locality within the Glass Buttes region. Only a very small percentage of the obsidian there is suitable fire material. (Weldon and Renfro, 2023)

I had gone to Glass Buttes looking for obsidian.

I had come home with a stone capable of holding nearly every color of a rainbow.

I did not yet know there was an old story from Glass Buttes about exactly that.

People Still Come for the Glass

Glass Buttes has been drawing people into this country for a very long time.

Today, one of its better-known traditions is the Glass Buttes Knap-in, an informal gathering held in the spring. Flintknappers and others interested in traditional stoneworking camp in the area, shape obsidian, demonstrate techniques and share what they know. It is not a Bureau of Land Management-sponsored event, but a gathering that has developed around a shared interest in the stone itself. The gathering continued in 2026. (Puget Sound Knappers Association, 2026)

There could hardly be a more appropriate place for it.

People have been working obsidian at Glass Buttes for thousands of years.

Archaeological research has traced human use of these obsidian sources back approximately 14,000 years. Quarry areas, camps, stone-working locations and other archaeological sites remain across the surrounding landscape. (Stueber and Skinner, 2015)

Obsidian fractures in a way that allows a skilled person to create an exceptionally sharp edge. It could be shaped into projectile points, knives and other tools, making a dependable source of high-quality volcanic glass valuable.

And Glass Buttes obsidian did not remain at Glass Buttes.

Every volcanic source leaves its own chemical signature in the glass. Modern analysis allows archaeologists to compare an obsidian artifact with known geological sources and, in many cases, determine where the material originated.

Through that work, Glass Buttes obsidian has been identified at archaeological sites hundreds of miles from central Oregon. Its presence across a wide area shows how far material from these buttes traveled through human movement and exchange. (Stueber and Skinner, 2015)

Long before Highway 20 crossed the high desert, people already knew there was something here worth traveling for.

And somewhere in that long history, the colors inside the glass became part of a story.

Bright rainbow descending toward the Oregon landscape after rain, photographed through a rain-covered windshield. — A rainbow reaches toward the Oregon landscape after a passing rain. At Glass Buttes, an old story tells of a rainbow descending into the earth and leaving its colors behind in the obsidian.

The Rainbow That Went Into the Mountain

Nearly a century ago, an unusual story about Glass Buttes appeared in print.

P. L. Forbes recorded it in 1935 in an account concerning iridescent obsidian. Smithsonian mineralogist Sydney H. Ball repeated it in 1941, and Craig Skinner later included it while writing about the obsidian of Glass Buttes. (Forbes, 1935; Ball, 1941; Skinner, 1983)

The story begins with fire.

According to the old account, a fire was set around the mountain to destroy troublesome yellow jackets.

For days, the mountain burned.

Then the weather changed.

Rain began to fall across the high desert, and a rainbow appeared over the mountain.

It did not simply brighten the sky and disappear.

The rainbow remained over one particular place throughout the day.

As evening approached, it seemed to descend toward the earth.

Then it disappeared into the ground.

After the fire had passed, people returned to the mountain. They found glass that could be worked into arrow and spear points.

But the place where the rainbow had entered the earth was different.

Its colors had remained behind.

The rainbow was now in the glass.

The surviving published accounts leave one important part of this story uncertain. They do not clearly identify the Native community from which Forbes originally received it. Glass Buttes lies within the ethnographic range of Northern Paiute people, but geography alone is not enough to attribute this particular story to them. Skinner also treated the attribution cautiously when he later reproduced the account. (Skinner, 1983; Stueber and Skinner, 2015)

The name of the person who first told it may be lost.

But the image survived.

A mountain burning beneath an Oregon sky.

Rain crossing the high desert.

A rainbow lingering over one place until evening.

Then descending into the earth and leaving its colors behind in black volcanic glass.

Fire Obsidian

The old story gave those colors one explanation.

Modern science eventually found another.

In 2007, Chi Ma, George Rossman and James Miller published a study of fire obsidian from Glass Buttes. Instead of looking only at the colors visible on the stone, they examined what was happening inside the volcanic glass.

What they found was remarkably small.

Fire obsidian contains extremely thin internal layers associated with concentrations of nanometer-sized magnetite crystals. Some of those layers are only about 300 to 700 nanometers thick. (Ma, Rossman and Miller, 2007)

Light interacting with these layers creates thin-film interference.

It is an optical effect capable of producing a broad spectrum of color. Depending on the stone, its internal structure, the light and the viewing angle, fire obsidian can display brilliant reds, oranges, yellows, greens, blues, violets and shifting combinations between them. (Ma, Rossman and Miller, 2007; Weldon and Renfro, 2023)

The colors are not painted onto the stone.

They are not created by polishing.

They are already inside the glass.

Cutting and polishing can reveal the internal layers at an angle that allows light to reach them properly.

That is why a piece can sit in my hand looking almost entirely black until I move it.

Then the colors appear.

An Old Story and a Modern Answer

It would be easy to take the old rainbow story and declare that it was describing fire obsidian.

The evidence does not allow me to do that.

The historical accounts refer to colored or iridescent obsidian from Glass Buttes. Fire obsidian has a more specific modern mineralogical meaning, and there is no way to know exactly which variety of obsidian inspired the old story.

The story is more interesting when left as the record gives it to us.

Someone noticed extraordinary colors in the dark glass of Glass Buttes long before anyone could examine that glass through a microscope.

They did not know about magnetite crystals or thin-film interference. They could not measure layers only a few hundred nanometers thick.

They simply knew what they could see.

There were colors inside the glass.

And the old story said a rainbow had put them there.

Collecting at Glass Buttes

The obsidian shown with this article is material I personally collected during my own visit to Glass Buttes.

The Bureau of Land Management identifies the Glass Buttes obsidian area within its Prineville District as an area used for recreational rock collecting. That does not mean every piece of ground around Glass Buttes is open to collecting. Private property, mining claims, closures, restricted areas and cultural sites can have different rules. Anyone planning to collect should verify current land ownership, boundaries, mining claims and BLM regulations before removing material. (Bureau of Land Management, 2024)

Archaeological material is protected.

Projectile points, worked stone, tools and other archaeological or historic objects found on federal land should remain where they are found. (Bureau of Land Management, 2024)

I am describing what I personally collected during my visit, not telling anyone else where they may collect.

The pieces shown here are naturally occurring obsidian that I collected and later had cut and polished.

And it was only after that work was done that I really understood what I had brought home.

Long polished piece of dark fire obsidian collected at Glass Buttes, Oregon, with a narrow iridescent layer visible beneath the surface. — Not every angle reveals the rainbow. In this piece of polished Glass Buttes obsidian, only a narrow trace of iridescence is visible within the dark glass.

The Treasure Outside

I have always liked the idea that treasure does not necessarily have to be buried, valuable or deliberately hidden.

Sometimes it is simply something remarkable that was already there.

Glass Buttes gave me one of those.

I can hold one of my polished pieces in my hand and see almost nothing but black volcanic glass.

Then I turn it toward the light.

Color appears.

Red, orange, yellow, green, blue and violet can emerge from the darkness, along with gold, bronze and shifting shades between them. Move the stone again and they can vanish as quickly as they appeared.

There is a scientific explanation for all of it, and it is extraordinary enough without embellishment.

The volcanic glass formed millions of years ago. Hidden within it are structures so small they are measured in nanometers. Light reaches those layers and the colors become visible.

But long before anyone could see or measure any of that, there was another explanation at Glass Buttes.

A mountain burned.

Rain came across the Oregon high desert.

A rainbow appeared and remained over one place until evening.

Then it went into the earth.

Perhaps when Oregon’s rainbows disappear from the sky, they have not disappeared at all.

Rainbow glowing through raindrops on a windshield beneath a dark Oregon storm sky. — A rainbow appears through the last of an Oregon rainstorm. An old Glass Buttes account gives the familiar sight an unusual ending: the rainbow does not simply fade from the sky, but descends into the earth.

Perhaps Glass Buttes is simply where they go to hide, waiting inside the dark volcanic glass for the light to find them again.

M. Hayward
Lost Cabin Mine

References

Ambroz, Jessica A., Michael D. Glascock, and Craig E. Skinner. “Chemical Differentiation of Obsidian within the Glass Buttes Complex, Oregon.” Journal of Archaeological Science, vol. 28, 2001, pp. 741–746.

Ball, Sydney H. “The Mining of Gems and Ornamental Stones by American Indians.” Bureau of American Ethnology Bulletin 128, Anthropological Papers No. 13. Smithsonian Institution, 1941.

Bureau of Land Management. Rock Collecting Guide: U.S. Bureau of Land Management Oregon & Washington. U.S. Department of the Interior, 2024.

Forbes, P. L. “Iridescent Obsidian.” The Gemmologist, vol. 4, no. 46, May 1935, pp. 306–309.

Ma, Chi, George R. Rossman, and James A. Miller. “The Origin of Color in ‘Fire’ Obsidian.” The Canadian Mineralogist, vol. 45, 2007, pp. 551–557.

Puget Sound Knappers Association. Glass Buttes Knap-in Event Information, 2026.

Skinner, Craig E. Research concerning Glass Buttes obsidian and the recorded Glass Buttes rainbow account, 1983.

Stueber, Daniel O., and Craig E. Skinner. “Glass Buttes, Oregon: 14,000 Years of Continuous Use.” In Toolstone Geography of the Pacific Northwest, Archaeology Press, Simon Fraser University, 2015, pp. 193–207.

Weldon, Robert, and Nathan Renfro. “Fire Obsidian’s Beguiling Spectrum.” Gems & Gemology, vol. 59, no. 2, Summer 2023.