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Petrology of the Volcanic Rocks of the Region Around Boulder Dam


Sklar, Maurice (1938) Petrology of the Volcanic Rocks of the Region Around Boulder Dam. Master's thesis, California Institute of Technology. doi:10.7907/3GPB-8K58.


The rocks around Boulder Dam, which range from pre-Cambrian to Recent in age, are dominantly volcanic, but other rock types occur.

Pre-Cambrian granitic rocks occur in the Black Mountains, to the east; at Saddle Ridge is a chloritic schist, also pre-Cambrian. No known Paleozoic or Mesozoic rocks occur within the area.

The oldest of the early Tertiary (?) rocks is the Altered Monzonite Porphyry (?), which occupies a belt trending east-west across the area. This formation has been quite thoroughly hydrothermally altered. Intrusive into it is the Quartz-Monzonite, which occurs mainly south of Hemenway Wash.

The Older Volcanic Series, the most extensive formation in the area, occurs on both sides of Hemenway Wash, and south of Boulder Dam. It consists of a tilted series of adesite flows and intercalated sedimentary breccias. Between it and the Younger Volcanic Series, in Black Canyon, occurs the sedimentary formation, the Dam Breccia.

The Younger Volcanic Series occupies a depressed and tilted block, penetrated by Black Canyon, and rests uncomformably or by fault contact on the Older Volcanic Series, and the Dam Breccia. It consists of four volcanic extrusive and intrusive members, two tuff members, and two inter-volcanic sedimentary breccias. The volcanic members are all generally latitic in composition, being high in potassa and in total alkalies. These volcanic rocks are differentiation products of one primary magma.

The Fortification Hill Basalt and the conformable underlying Muddy Creek Formation are Pliocene, or possible Pleistocene, in age. Quaternary deposits include terrace gravels of the Colorado River, and recent alluvium.

Item Type:Thesis (Master's thesis)
Subject Keywords:Geology
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Campbell, Ian
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1938
Record Number:CaltechTHESIS:04192010-112518708
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5722
Deposited By: Tony Diaz
Deposited On:19 Apr 2010 19:03
Last Modified:03 Oct 2019 23:46

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