Simcoe Mountains facts for kids
The Simcoe Mountains Volcanic Field is a cool area in south-central Washington state, United States. It's east of Mount Adams. This field has many old volcanoes and lava flows.
A big part of the Simcoe Mountains is inside the Yakama Indian Reservation. Even though it's near the famous Cascade Arc volcanoes, the Simcoe Mountains Volcanic Field is much older. It's a different type of volcanic area called an intraplate field. This means its volcanoes formed away from the usual places where tectonic plates meet.
Tallest Spots in the Simcoe Mountains
Most of the volcanoes here are like small hills, rising about 75 to 250 meters above the land. But one, called Signal Peak Shield, is much taller. It stands about 500 meters above its surroundings!
Here are some of the highest peaks in the Simcoe Mountains:
- Jennies Butte (1,954 meters or 6,410 feet): This is a dacite cone.
- Indian Rock (1,775 meters or 5,823 feet): This is a basaltic shield volcano.
- Castle Rock (1,724 meters or 5,656 feet): Another basaltic shield volcano.
- Signal Peak Shield (1,555 meters or 5,100 feet): This mafic shield volcano is about 5.7 million years old.
How the Simcoe Mountains Formed
The Simcoe Mountains Volcanic Field sits in an area called the Yakima Fold Belt. This area is part of the larger Columbia River Basalt Group. The volcanoes here erupted in three main periods. These eruptions happened during the Pliocene and Quaternary geological times.
- The first period was about 4.2 to 3.2 million years ago.
- The second period happened from 2.2 to 1.2 million years ago.
- The most recent period was from 1.0 to 0.6 million years ago.
The very last eruption in this field was a lava flow called the "Trachybasalt of Pretty Swamp." Scientists think this eruption happened about 631,000 years ago.
Some of the volcanic activity in the Simcoe Mountains happened at the same time as eruptions in other nearby areas. For example, the Goat Rocks area to the northwest was also active. Also, for the last 350,000 years that Simcoe was erupting, there was activity in the Mount Adams region. However, Mount Adams itself had not yet started to form.
Another volcanic area, Indian Heaven, is to the west. It is generally much younger than Simcoe. Indian Heaven only became active during the last 200,000 years of Simcoe's activity. And a very famous volcano, Mount St. Helens, formed entirely after the Simcoe Mountains Volcanic Field stopped erupting.
