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NPS Form 10-900 OMB No. 1024-0018
(Rev. 8-86)
United States Department of the Interior
National Park Service

National Register of Historic Places
Continuation Sheet

Section number 8 Page 14

St. Francis Dam (Site of), Los Angeles County, California — Narrative Statement of Significance
[continued]
The magnitude of the St. Francis Dam disaster brought engineers and geologists together from all over the country to theorize about
why the disaster occurred, and what measures should be implemented to prevent future occurrences of its kind. Thirteen different
panels were convened to investigate the St. Francis failure. The principal investigative body, the Governor’s Commission, may have
fixed the specific geological conditions and engineering causes of the failure incorrectly, but the panel did identify the weakness in a
system that provided for little oversight of design and construction. The consensus of opinion which emerged among engineers and
others was that, “state regulation of the construction of all dams — municipal as well as private — was imperative.” [Western
Construction News, 1929: 203]

In the wake of the disaster, new dam safety legislation was adopted by the California Legislature on August 14, 1929, strengthening
the existing laws and centralizing authority. Where previously the control of dam construction had been spread out among several
agencies, each with varying degrees of supervision, the State Engineer was now provided with authority to review, supervise and
maintain all non-federal dams greater than 25 feet high or which impounded at least 50 acre feet of water. In addition, funding was
provided for a comprehensive three-year survey and inspection of all existing dams. The new and far more aggressive California dam
safety legislation would become a model for other states to follow. [Western Construction News, 4-25-1929; Rogers, 1995: 82-4]

The legislature created a new division of State Engineering Department under the supervision of the State Engineer. Trained personnel
were selected to carry out the task of reviewing the safety of dams through extensive testing, including field examination, stress
analysis and computation. A total of some 830 dams were inspected. The results showed that only one-third of the dams could be
viewed as satisfactory in terms of safety; one-third required further investigation and one-third were in need of repair. Those dams
identified as unsafe were rehabilitated. [Hawley, 1936]
This more conservative approach to dam building and design led to immediate changes in the planning and construction of new dams.
The first project to be effected was the ambitious San Gabriel Forks Dam, planned by the Los Angeles County Flood Control
District on a site immediately below the confluence of the east and west forks of the San Gabriel River in the Angeles National
Forest. This concrete arch dam, at 425 feet high and 1,700 feet across, was to be the largest concrete structure in the world. It was
designed to impound a reservoir of 240,000 acre feet, a quantity over six times greater than the St. Francis Reservoir.

Construction on the San Gabriel Forks Dam began in the Spring of 1929, but was halted in September when a massive landslide
occurred during the excavation of the dam’s western abutment. Construction was halted, and the State Engineer called in to
investigate the feasibility of continuing. The State Engineer’s Office report, issued only three months after the creation of the
department’s duties by the Legislature, called for the abandonment of the concrete arch dam due to the geological instability of the
site, and the construction of three, smaller rock-fill dams on the river in its stead.
As a result, the County of Los Angeles would lose nearly its entire investment of $4.5 million on the project, and one Los Angeles
County supervisor would be jailed on a related bribery conviction. The new state oversight law had its first test, and in dramatic
fashion, potentially averted a catastrophe of a magnitude that would have dwarfed the St. Francis Dam disaster.
Ultimately, two of the three proposed alternative dams were built on the San Gabriel River, but not without the the hand of the State
Engineer being felt once again. Further exercising its new powers, the State Engineer in 1935 rejected one of the District’s proposed
designs for San Gabriel No. 1, the first of two rock-fill dams to be constructed on the river. [Baumann, 1941: 1595, 1635-7]