Saturday, May 14, 2016

Non Washington: Aerial Notes from Nevada

Flying into Las Vegas, Nevada is a always a great treat for a geologist with a window seat or for anyone that appreciates landscapes.

A top highlight is the classic Keystone Thrust:

The older rocks of the layered limestone rocks of the gray Cambrian-age Bonanza Formation are overlying the buff to red sandstone of the younger Jurassic-age Aztec Formation. The older rocks were thrust up and over the younger rocks approximately 70 million years ago with an estimated crustal shortening of 60 miles. There are plenty of thrust faults in Washington State, but not nearly so well exposed and easily seen.

To the west of the thrust fault, the older rocks are also folded. Again demonstrating the crustal shortening or compression that took place in this area.

Geologic hazards are also readily observed, such as flood hazards. Nevada is full of alluvial fan areas with associated flood, erosion and sediment deposition hazards.

Dam and excavation on right to capture and hold water and sediment to protect Las Vegas development on the left.

Parhump has seen rapid residential development with very little regard to flood hazards associated with alluvial fans. The approach to development appears to have been build first and then solve the flood hazards after floods take place. Parhump experienced flooding in 1997 and twice in 2003 including flood waters as deep as 3 to 4 feet (Nevada Division of Water Resources, 2013).

Efforts to assess the hazards have included detailed mapping of piedmont and playa features (House, Buck and Ramelli, 2010). The broad fan below shows a variety of ages on its surface and illustrates the fact that alluvial fans are complicated and subject to change during flood or debris flood events.

The Las Vegas River has caused flooding and erosion in Las Vegas that has led to a variety of flood projects on the river. But given the drought risk that Las Vegas lives with, water in the river is a good thing. That water is actually waste water from the waste water treatment plant. The water is simply being returned to where it was drawn from.

Flowing water in the Las Vegas River

The long drought is evident when Lake Mead came into view.

Bath tub ring around Lake Mead on the Colorado River

Nevada is well know for mining. Part of the fun of flying over the state is mine spotting. Below is a the classic gold mine operation with heap leaching to extract the gold from the ore:

See SF's post for some geology and other references for this area

Nevada has non metal mines as well including mountain top mining for limestone and mountain top development.

Limestone mine outside of Las Vegas for cement production

Building pads for home development in south Las Vegas 

The biggest recent alteration of the landscape of Nevada the past few years has been huge solar farms:

Distant view of solar farm 

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