GCBCJXM Mount Washington (Earthcache) in Oregon, United States created by Chet13

GCBCJXM ▼

A cache by Chet13 Message this owner

Hidden : 9/7/2025

Difficulty:

Terrain:

Size: Size: other (other)

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Geocache Description:

Welcome to Mount Washington

Welcome to central Oregon, where you can see one of the most striking peaks in the Cascade Range, Mount Washington. This spire-like mountain rises above the surrounding High Cascades lava fields. At 7,794 feet, it is not the tallest in the region, but its sharply jagged shape makes it highly distinctive on the skyline. The peak you see today is what remains of a much larger volcano from the Pleistocene. Over thousands of years, glaciers and erosion have carved away much of the original cone, leaving the dramatic, rugged spire that dominates the view.

The Story Behind Mount Washington

Mount Washington formed during the late Pleistocene epoch, less than a few hundred thousand years ago. The Pleistocene, often called the Ice Age, was a period of repeated glaciations between about 2.6 million and 11,700 years ago. Unlike Mount Whitney, which is made of granite that cooled slowly underground, Mount Washington is a volcanic peak built from dark lava rocks called basalt and basaltic andesite. Basalt forms when very fluid lava cools quickly at the surface, while basaltic andesite is a thicker, slower-flowing lava with a little more silica. These lavas erupted from cracks known as fissures and from openings in the crust known as vents. The magma that fed these eruptions came from two processes. One was the subduction of the Juan de Fuca Plate beneath the North American Plate, which caused rock deep in the mantle to melt. The other was intra-range rifting, in which the crust of the Cascades was pulled apart, creating extra pathways for magma to rise.

The volcano is part of the Sisters Reach, a 56-mile-long chain that contains more than 466 volcanoes. Geologists debate whether Mount Washington is best described as a steep-sided shield volcano or as a mafic stratovolcano. A shield volcano usually has broad and gently sloping sides, but Washington’s flanks are steeper than those of classic examples. A stratovolcano is a cone-shaped mountain made of alternating lava and volcanic debris. Mafic means that its lavas are rich in magnesium and iron, which gives them a dark color. Whatever its label, Washington was built by overlapping lava flows, layers of loose volcanic fragments called pyroclastic deposits, and a central volcanic plug of hardened lava that filled its main vent. This plug is made of especially strong rock, which resisted erosion more than the rest of the cone.

During the Ice Ages, thick glaciers eroded Mount Washington, carving away softer volcanic layers and leaving the jagged spire that stands today. Glaciers are slow rivers of ice that grind and pull rock as they move downslope, shaping features such as cirques, which are bowl-shaped basins at the heads of valleys, and wide U-shaped valleys. From the Mount Washington Viewpoint, you can see how its pointed profile resembles Switzerland’s Matterhorn. For this reason it is grouped with Oregon’s other Matterhorn-like peaks such as Mount Thielsen, Three Fingered Jack, and Mount Bailey. All of these volcanoes erupted briefly, went extinct more than one hundred thousand years ago, and were sculpted by glaciers into dramatic pinnacles. Mount Washington’s rugged shape tells the combined story of both fire and ice. Volcanic forces built it, and glacial forces carved it into the peak we see today.

Tasks for This EarthCache

To log this EarthCache, visit the site and complete the following tasks. Send me your answers via Geocaching or email.

Include "Mount Washington - GCBCJXM" on the first line of your message.
From this viewpoint, describe Mount Washington’s profile. Does it appear sharp and spire-like, broad and sloping, or cone-shaped?
Look for glacial features such as cirques, U-shaped valleys, or steep ridges carved by ice. Identify one and explain how it shows that glaciers helped shape this mountain.
Examine the color and texture of Mount Washington’s rock. Does it look light or dark, smooth or jagged? What does that reveal about its formation and weathering?
Based on your observations, do you think Mount Washington is a steep-sided shield volcano or a mafic stratovolcano?
In your log, attach a photo of yourself or a personal item at the posted coordinates with Mount Washington in the background. (Note: photos predating the publication of this EarthCache are not accepted.)