The Geology of Crater Lake National Park

Like most of our national parks, the spectacular beauty of Oregon's only national park is a result of the geologic processes that created it. But whereas most of our parks were created by gradual processes over long periods of time—for example, erosion by the Colorado River to create the Grand Canyon—Crater Lake was created in a few days during a...

South Sister—the third highest volcano in Oregon and one of its youngest

The Three Sisters volcanoes, located in the Three Sisters Wilderness west of Bend, Oregon, are part of the Cascade Range of volcanoes formed above the Cascadia subduction zone. "For magnificence of glacial scenery, for wealth of recent lavas, and for graphic examples of dissected volcanoes, no part of this range surpasses the area embracing the Sisters and McKenzie Pass", said...

How does the Rogue Valley fit into the larger tectonic picture?

In the last three posts, we explored the geologic makeup of the Rogue Valley region. Most people know that there is a subduction zone off the coast of the Pacific NW and you might wonder: how does the Rogue Valley region fit into this larger picture? We will explore the tectonic setting in this post. This diagram shows the present...

Sedimentary rocks tell stories about the Rogue Valley region’s geologic history

In the previous two posts, we explored the distribution of rock units in the Rogue Valley region, and how the different resistances of these rock types to weathering and erosion has created the topographic variations we see in the landscape. The different rock types also produce a large variety of soil types that are important for gardeners and vintners in...

Why is the Rogue Valley a valley?

In the April 19 post, we examined the geologic units that are exposed in the Rogue Valley region, and saw that the units are all tilted toward the NE, with the oldest units located to the SW (between the valley and the coast), and the younger units located toward the NE (toward the active volcanoes of the High Cascades like...

The Rogue Valley region in SW Oregon: displaying 300 million years of geologic time

Typically, I post blogs when traveling away from my home in Ashland, Oregon. But with COVID-19 keeping us all at home, it seems a good time to investigate the landscape of my local region. Ashland is a tourist town best known as the home of the Oregon Shakespeare Festival (OSF), an eight-month season of 11 plays—four by Shakespeare and seven...

What is so special about the Cascade-Siskiyou National Monument?

This national monument spans the border between Oregon (Jackson County) and California (Siskiyou County) immediately east of the I-5 freeway. It was first established in 2000 by President Bill Clinton and expanded in January 2017 by President Obama as one of his last actions before leaving office. The monument is managed by the Bureau of Land Management (BLM) from the...

Human interactions with the Lava Beds landscape

The Modoc group of Native Americans have lived in the region that is now the Lava Beds National Monument for thousands of years. They left little imprint on the land, but they did leave some rock art that is interesting to examine. Two caves—Big Painted Cave and Symbol Bridge Cave—contain pictographs that are painted onto the rocks with a charcoal-based...

Lava lava everywhere—Lava Beds National Monument, NW California

I've said there are just two Cascade Range volcanoes in California—Mt. Lassen and Mt. Shasta. But there is a third called Medicine Lake Volcano, as shown on the map below (from https://en.wikipedia.org/wiki/Cascade_Volcanoes). Lava Beds National Monument is located just north of the volcano, where numerous flows have completely covered the landscape during the past 500,000 years. Because it is a...

Climbing Mount McLoughlin—one of the lesser known Cascade volcanoes

Mount McLoughlin is located 63 kilometers (38 miles) east of Ashland, Oregon, where I now live. As shown on this map by the U.S. Geological Survey, Mount McLoughlin is located between the volcanoes of Mount Shasta and Crater Lake, which is the remnant of Mount Mazama that exploded to become a caldera 7,700 years ago. All of the Cascade Range...

About the Blogger

Karen (here with Mt. Shasta in background) is a geology professor emerita who aims to provide a "pocket geologist" for world travelers. Follow the blog to explore the landscapes of our planet and figure out what causes them to look the way they do.

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