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The Geology of the East Coachella Tunnel of the Metropolitan Water District of Southern California. A San Diego Fauna in the Vicinity of Val Verde, California


MacLellan, Donald Dominic (1936) The Geology of the East Coachella Tunnel of the Metropolitan Water District of Southern California. A San Diego Fauna in the Vicinity of Val Verde, California. Dissertation (Ph.D.), California Institute of Technology.


The Geology of the East Coachella Tunnel of the Metropolitan Water District of Southern California:

The following paper describes the geology of the East Coachella Tunnel of the Metropolitan Water District of Southern California. This tunnel extends along the southern flank of the Little San Bernardino Mountains, in Riverside county, California.

Four rock types were encountered in the excavation of the tunnel: a regionally metamorphosed series of schists and gneisses of sedimentary origin, here called the Berdoo series; granitoid rocks resulting from replacement, called the Thermal Canyon series; a grananitic intrusive called the Fargo granite; and bench gravels.

The Berdoo series is divisible on the basis of lithology into three facies: a dark thin-bedded feldspathic and biotitic schist, a light gray feldspathic gneiss, and a medium gray coarse grained schist which is transitional between the first two.

The Thermal Canyon series consist of massive granitoid rocks which are of the mineralogical composition and general aspect of quartz-diorites.

Between these two rock series occurs a transition zone of from 1000 to 6000 feet in width within which, as examined in the field, the sedimentary textures and structures which characterize the Berdoo series appear to gradually give way to the massive granitoid textures of the Thermal Canyon series. Petrographic studies reveal the existence of a zone of mineralogical gradation between the two series within which the assemblage which constitutes the Berdoo series gradually becomes replaced through recrystallization by that which constitutes the Thermal Canyon series. The minerals of the recrystallized assemblage are not conformable to definite surfaces such as bedding, but instead show the fortuitous orientation of an igneous rock. Also, the plagioclase feldspars of the recrystallized assemblage are slightly more calcic than those of the Berdoo series.

Chemical analyses show that the composition of the two rock series is very nearly the same, excepting for a progressive increase in lime, and corresponding decreases in ferric iron and potassa with advancing recrystallization.

The results of field, petrographic, and chemical methods of investigation thus indicate that the Thermal Canyon series rocks resulted trough recrystallization of a portion of the Berdoo series rocks. Ascending hot solutions and gases of magmatic origin are postulated as the actuating agencies in the recrystallization.

The Fargo granite occurs as an intrusive stock in the east central portion of the area, and consists of a pinkish gray coarsely crystalline rock of about the mineralogical composition of a quartz-monzonite.

The chief structural feature of the area is faulting, of which two systems are recognizable, one which trends easterly, and one which trends northerly. Two successive periods of domical uplift in the south-eastern portion of the area are postulated as causes for the faulting.

The geological aspects of tunnel excavation, with especial reference to the influence of structure, are discussed briefly.

A San Diego Fauna in the Vicinity of Val Verde, California:

Within the lowermost beds of the Saugus group in the Santa Clara Valley region as mapped by Kew (1) occur a series of conglomeratic and arenaceous sediments which have been known to carry a marine fauna, the age of which has not in every case been definitely determined. Mr. W. P. Popenoe of the California Institute of suggested to the writer that a study of certain exposures of these sediments be made with an especial view towards determining their age, and whether they constituted a geologic formation distinct from those of both the Pico and Saugus groups as previously mapped. The findings of this study are herewith presented.

Item Type:Thesis (Dissertation (Ph.D.))
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 1936
Additional Information:Minor thesis included, pp. [105-115]: A San Diego Fauna in the Vicinity of Val Verde California.
Record Number:CaltechTHESIS:04132010-082926337
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5716
Deposited By: Tony Diaz
Deposited On:13 Apr 2010 16:00
Last Modified:19 Dec 2017 23:49

Thesis Files

PDF (Full thesis) - Final Version
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PDF (Plae 1. Geologic map, East Coachella Tunnel Area) - Supplemental Material
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PDF (Plate 2) - Supplemental Material
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