Geology
The Mission Mountains are composed largely of what is called "Belt Rock" from the Belt Supergroup. The sedimentary rocks in this group are believed to have been formed between 1.47 and 1.4 billion years ago in what geologists David Alt and Donald Hyndman call the Belt Basin. The roughly circular basin collected sediments from surrounding areas for millions of years. The basin was eventually buried and later re-exposed through the collision of several tectonic plates around 80 million years ago. Other sources say the rocks where exposed about 100 million years ago.
Much of the Belt Rock found in the Mission Mountains is a crumbly sedimentary rock known as mudstone. The mudstone in the Belt supergroup is often characterized by mudcracks, which points to it being formed while wet, drying, cracking then and being repeatedly flooded with new wet material that also dried and cracked.
Most of the rock in the Mission Mountains hails from the end of the Proterozoic Eon, towards the end of what is called Precambrian time. Because they are so old, the only evidence of life in the rocks are algae blooms and very basic plant fossils. These organisms played, however, the important role of converting carbon dioxide in the water into oxygen that was pumped into the acidic and poorly oxygenated atmosphere.
The color of the mudstone in the Missions has much to do with the presence of the mineral hematite during the its formation. Hematite is formed by iron particles' reaction to oxygen in the atmosphere. Green and gray stones found in the Missions were most likely formed in deep water, the red in more shallow water. Ripple marks can be found in much of the rock; they would have formed mostly in shallow water with gentle waves.
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