Hayrick Butte is a tuya

Tuya

A tuya is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are somewhat rare worldwide, being confined to regions which were covered by glaciers and also had active volcanism during the same time period.-Formation:Tuyas are...

 volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 in the Cascade Range of northern Oregon, located near Santiam Pass

Santiam Pass

Santiam Pass is a mountain pass in the Cascade Range in central Oregon in the United States. It is located on the border between Linn and Jefferson counties, about northwest of Sisters, between the prominent volcanic horns of Three Fingered Jack to the north and Mount Washington to the south...

 just west of the Cascade Crest. It is adjacent to the cinder cone

Cinder cone

According to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...

, Hoodoo Butte

Hoodoo Butte

Hoodoo Butte is a cinder cone butte in the Cascade Range of northern Oregon, located near Santiam Pass just west of the Cascade Crest. A ski area, also named Hoodoo, is located on the northwest through northeast flanks of the cone, and the summit area includes the top stations of two chairlifts...

, which overlaps its western edge.

A tuya is a type of subglacial volcano

Subglacial volcano

A subglacial volcano, also known as a glaciovolcano, is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava...

, formed when lava erupts underneath an overlying glacier

Glacier

A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

 or ice sheet

Ice sheet

An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...

 and then melts through to the surface and pools, producing the flat plateau on top with near-vertical walls along the ice-contact margin as the lava cools and hardens. Hayrick Butte is one of the most perfectly formed examples of a tuya in the contiguous United States

Contiguous United States

The contiguous United States are the 48 U.S. states on the continent of North America that are south of Canada and north of Mexico, plus the District of Columbia....

with a nearly flat triangular plateau about 0.5 mile (0.80467 km) across and steep walls rising about 700 foot above the plain below.