Inherent skepticism leads me to suspect that the financial interests of someone, or group of someones, might have played more of a role in siting at this location than engineering considerations.
I'll admit to being unfamiliar with the area's geology, but ER's research above hints at a sort of Rube Goldberg approach to making it all fit just here, as opposed to somewhere the topology might have been better suited.
/venality theory
https://archive.org/stream/zh9californiastatew2003calirich/zh9californiastatew2003calirich_djvu.txt
In the late 1940s, the State compared development
at the Oroville site with developments on the North
Fork at Big Bend and on the South Fork at Bidwell
Bar. The conclusion, quoting the August 1949 report
(see Bibliography), was that “major storage capacity
can most feasibly and economically be provided at the
Oroville site”.
Work then was concentrated on feasibility studies
for the State Water Project (then known as the
Feather River Project), which was authorized by the
State Legislature in 1951. A concrete gravity dam
similar to Shasta Dam was assumed at Oroville for
these studies.
In 1956, the State Legislature authorized the prepa-
ration of final designs, plans, and specifications for
Oroville Dam. First, the type of dam to be constructed
at the site had to be selected. Initially, gravity, multi-
ple-arch, straight-buttress, and arch-buttress concrete
dams were studied (Figure 58).
One of these designs was of the concrete-buttress
65
Figure 58. Model of Multiple-Arch Concrete Don
66
type consisting of a series of massive head buttresses
60 feet thick and spaced 1 20 feet center to center across
Oroville Canyon. Later, to eliminate the extremely
high buttresses that would have been required in the
deeper part of the Canyon, an arch-buttress alterna-
tive was developed. The central deepest portion of the
Canyon was to be spanned by an inclined arch abut-
ting against a massive buttress on either side. The
remainder of the dam would have consisted of a mas-
sive head buttress similar to that proposed for the
straight-buttress dam. Preliminary design studies of
this hybrid dam showed it to be economically and
engineeringly attractive. Detailed design studies,
which included a structural model, were undertaken.
Designs for multiple-arch dams were suggested by the
foremost concrete dam designers in the world at the
time.
The Oroville Dam Consulting Board (discussed in
Appendix A) advised the Department of Water Re-
sources on these studies and on the final design and
construction of the Dam and appurtenant structures.
Concurrent with these design studies, extensive
damsite geologic and construction materials investiga-
tions were being undertaken. The materials investiga-
tions were centered in the vast fields of tailings located
10 to 15 miles downstream of the site that had been
produced by dredgers working over the flood plain of
the Feather River for gold. This gravelly cobbly
material originally was explored for a source of con-
crete aggregate and later proved to be an ideal material
for pervious shells for the earthfill dam. The dredger
tailings, consisting of washed sands and gravels, var-
ied in depth from IS to 50 feet. Normal dredger opera-
tion stacked the gravel and cobbly material on top of
the sand. The sand deposit was not usable for concrete
aggregate but could be used to blend with the tailings
to form transition zones for an earth or rockfill dam.
http://www.freerepublic.com/focus/news/3524221/posts?page=1391#1391
Gov. Moonbeam’s father lied about the cost of the dam to get the bond issue passed.