A Short Geologic History of Cache Valley
During the summer of 2011 my sister Cheri Mickelson asked me to present a short geological lesson to her first grade class. They were familiar with Cache Valley, their home, so I decided to make it a brief history of their valley.
First we need a few definitions and background material.
The study of rocks and earth
The study of fossils
The study of ancient people - cultures and way of life
Types of Rocks
Geologists generally recognize three kinds of rock:
These rocks are formed in volcanoes and underground magma. Examples are:
|Obsidian||Tuff or Volcanic Ash||Granite|
These rocks are generally layered and formed in water or on the earth's surface
|Coal (peat - vegatation)||Limestone (shells and remnants of other sea plants and animals)||Sandstone (beaches and dunes)||Shale (mud)|
These rocks have been altered as a result of great pressure and temperature.
|Marble (from limestone)||Gneiss (perhaps Granite)||Slate (from Shale)|
How Old is Old?
Some things that seem very old, are really very young when compared to other things around us. The lady is less than 100 years old. The temple is around 130 years old. The trees are redwoods, perhaps 1,500 years old. The mountains in the pictures on the right were formed 20 million years ago while the cliffs and ledges were formed as much as 500 million years ago.