Did You Know Saddle Rock Is Older Than The Cascades?

Saddle Rock - an iconic pair of giant rock pinnacles looming above Wenatchee. 

Seattle’s Public Broadcasting Station - KCTS 9 has an educational geology show called Nick on the Rocks. The host, Nick Zentner, is a professor of Geology at Central Washington University in Ellensburg.

How did Saddle Rock appear above Wenatchee?

Saddle Rock and the other pinnacles in greater Wenatchee result from volcanic activity.

It is believed to have formed 44 million years ago, older than the famous Cascade volcanoes.

It is interesting to know that Mt. St. Helens, Mt. Rainier, and Mt. Baker are all younger than the formations at Saddle Rock. 

What kind of rock makes up Saddle Rock?

Nick explained that the material that makes up the iconic pinnacles is not typical of volcanic rock. The rocks of Saddle Rock are rhyolite—pink volcanic rocks with little white chunks made up of smoky quartz and crystals. 

Rhyolite is stiff, sticky lava, so each pinnacle is a rhyolite dome. Nick Zentner’s origin story for the rhyolite is very descriptive.

‘A squirt of very toothpaste-like magma. It was part of a very explosive volcanic system.’ - Nick Zentner, CWU Geology professor.

 

Was there a Super Volcano underneath Wenatchee?

The 44 million-year-old rhyolite that makes up Saddle Rock has the same story as the many outcrops above ground and visible in the area. Wenatchee Dome, Castle Rock, Black Thumb, and Rooster Comb have the same rhyolite rock.

The older Cascades erupted above the surface due to a violent pyroclastic ash flow.  Nick explains that rhyolite outcrops probably came from some supervolcano rather than a composite cone volcano. The pinnacles of rhyolite lava were once underground fingers of magma that worked their way up through soft sandstones. Some of them got to the surface and exploded violently.

Geologists like Nick are still trying to work out the details.

Watch Nick tell this story here, and check out the many episodes of Nick on the Rocks that spin yarns about the varied and interesting geology in the great Pacific Northwest.