Geological Features Tour

Introduction and Welcome

Welcome to Geological Adventures, where we bring you to the science. We are delighted that you are interested in finding out more about the geology of our planet. Geology is more fun as you experience it first hand. Learning about the geology of our planet will help make clear the reasons why we should do all we can to protect it. On this tour we will be visiting both the east

and the west coasts of the continental United States. On our tour we will learn about many geological features, including volcanoes, ground water and caverns, and natural rock formations found on the coast.

Mount Shasta, California

Our first stop will take us to beautiful Northern California about 60 miles from the California-Oregon border and in the southern part of the Cascade Range. The Cascade Range has 15 main volcanoes of which Mount Shasta is the second highest with an elevation of 14,162 feet.

Mount Shasta is a composite type of volcano consisting of alternating layers of pyroclastic fragments, or explosively erupted volcanic rock, and solidified lava flows. Mount Shasta was built, as was other composite volcanoes, over enormous spans of time. Mount Shasta is believed to be more than 300,000 years old. Eruptions from composite volcanoes are intermittent with hundreds or thousands of years between eruptions. Mount Shasta last erupted in 1786. Even though Mount Shasta erupted more than 220 years ago it is still considered an active volcano.

As an active volcano, Mount Shasta has many things to explore and learn about. About 300,000 to 360,000 years ago the entire north side collapsed, creating an enormous landslide. Since that time Mount Shasta has been building. Mount Shasta has four distinct and overlapping cones waiting to be explored.

The Sargents Ridge cone is the oldest visible cone and extends southward from the peak of Mount Shasta. Dozens of lava flows and fragmental layers have worked to form this large cone some 100,000 to 200,000 years ago. The cone has a prominent rock feature called Thumb Rock, which when seen needs no explanation for the choice of the name (Topinka, 2007).

The Sargents Ridge cone is also the home of the Konwakiton Glacier, one of the smallest of the seven glaciers on Mount Shasta. The vent on this part of Mount Shasta is now extinct.

The Misery Hill cone consists of much of what we see when looking at Mount Shasta today. About 30,000 to 50,000 years ago a new vent opened, on the north side of the Old Sargents Ridge cone, erupted and partially buried it. The last volcanic event that added new material to the Misery Hill cone was a lava dome at its summit. The Misery Hill cone is a favorite among hikers and climbers (Topinka, 2007).

The Shastina cone is unique in that if it were by itself anywhere else in the Cascade Range it would be considered a major volcano. The Shastina cone is what gives Mount Shasta its double peak. The Shastina cone formed over 9,500 years ago and is home to Diller Canyon, which funneled a large pyroclastic flow about 9,230 years ago. This pyroclastic flow covers the ground that is now the town of Weed (Topinka, 2007).

The Hotlum cone is the youngest cone of Mount Shasta at around 6,000 to 8,000 years old. The Hotlum cone is also the highest cone and thus the summit of Mount Shasta. The Hotlum cone was named after the Hotlum Glacier on its northern face. The longest lava flow from is the Military Pass flow, which is 500 feet thick and extends five and a half miles down the northwest face of Hotlum cone (Topinka, 2007).

There are many myths and legends surrounding Mount Shasta. There are legends involving Lemurians, Atlanteans, Secret Commonwealth Citizens, dwarfs, fairies, Big Foot, and space beings that can materialize at will so to keep their identity secret. Mount Shasta has long been sacred to different Native American tribes such as Shasta, Modoc and Klamath. One myth from the Modoc and Shasta tribes as told by Ellie Crystal goes something like this “The Great Spirit created the mountain from above, cutting a hole in the sky and pushing down ice and snow until a mountain was formed that pierced the clouds. The Great Spirit then used the mountain to step onto the earth, creating trees and calling upon the sun to melt snow to provide rivers and streams. He breathed upon the leaves of the trees and created birds to nest in their branches. When he broke up small twigs and cast them into the streams, they became fish. He used branches to make animals and logs to make the large animals. The largest of these was the grizzly bear. The Great Spirit took up his abode on the mountain. His daughter, who fell from the mountain, was raised by grizzly bears and married one of their clan. Their children were the