Tucson Mountains EarthCache
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The Tucson Mountains are located to the west of the Tucson Valley.
The Tucson Mountains were once the top of a large volcano, the bottom of which is the Santa Catalina Mountains. The top of this volcano slid 20 miles (32 km) to the west, and the area between the Tucson and Catalina Mountains was dropped down to form the valley.
About 70 million years ago a huge volcano formed about where the Santa Catalina Mountains are today. The volcano collapsed in on itself, forming a circular basin called a caldera. Then 30 millions years ago detachment faults caused the upper part of the caldera to slide 20 miles (32 km) off the lower part of the caldera.
Faulting (to produce a fault also occurred causing valleys/basins and mountains/mountains ranges.
Where Tucson sits today dropped 10,000' (3300 m) or more to form the valley (which has since filled in with at least 5000' (1650 m) of sediment).
The upper caldera that was left higher than the valley became the Tucson Mountains. The lower caldera and underlying granite that was left higher on the north side of the valley became the Santa Catalina and Rincon Mountains.
Much of the Tucson Mountains is composed of rhyolite, an extrusive igneous rock that was created during the eruption of the volcano as where much of the Santa Catalina Mountains is composed of granite, an intrusive igneous rock from the solidified magma below the volcano.
Note: Some of the information found on this page was copied with permission from link
The answers to the following questions can be found on the neatby displays.
To log this earthcache as a find please answer the following and email me your answers:
1. What type of rock proves that both the Tucson Mountains and the Santa Catalina Mountains are from the same formation ?
2. How strong was the eruption that caused the volcano to erupt ?
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