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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 6

St. Francis Dam (Site of), Los Angeles County, California — Narrative Statement of Significance
[continued]
Given these conditions, San Francisquito Canyon would seem at the outset to have been a less than ideal choice for the location for a
high concrete dam. According to Mulholland’s later testimony, however, in 1912 additional geological investigations of the future
St. Francis Dam site undertaken by Mulholland and the noted Stanford University Geology professor John Casper Branner, assuaged
any reservations he might have had in his own mind about the suitability of the site. [Coroner’s Inquest, 1928]
The first formal survey of the dam site was conducted in 1922, and by May 1923 engineering plans for a 175-foot high concrete
gravity arch dam designed to retain 30,000 acre feet of Owens Valley water emerged from the Bureau of Waterworks and Supply.
Mulholland and his crew at the bureau evinced complete confidence in their abilities as dam designers and builders, justified by their
successful construction of some twenty dams by the time they began work in San Francisquito Canyon, including some of the
largest earth-fill dams in the world. The St. Francis Dam was the bureau’s first mass concrete dam, however, and represented a
number of design challenges that the bureau had not encountered in their prior efforts.

The St. Francis Dam was one of two concrete arch dams of similar design to come out of Mulholland’s office during this period. An
earlier “twin,” Weid Canyon Dam, was built in the Hollywood Hills in 1924. Shortly after its completion, this dam was renamed in
honor of William Mulholland, in recognition of his singular contributions to the development of water resources for the city.
[Mulholland, 2000: 281]
Even during the design stages of the St. Francis Dam, the bureau continued its race against the city’s steadily increasing demand for
water. In an effort to accommodate these needs, in July of 1923, the design capacity of the San Francisquito reservoir was increased
by nearly ten percent, to 32,000 acre feet, which was accomplished by raising the dam ten feet in height. This storage capacity figure
represented a one-year water supply for the City of Los Angeles at that time, meeting Mulholland’s principal design criterion for the
reservoir. By fixing on this goal, it would later become clear, Mulholland’s engineers were not only chasing a moving target, they
were incorporating serious flaws into the dam’s design. [Rogers, 1995: 26-7]

The construction of the St. Francis Dam commenced in April, 1924. Even as the dam began to rise, so did the city’s demand for
water. The bureau responded in July 1925 by increasing the dam’s height a further ten feet, expanding the reservoir’s storage capacity
to 38,168 acre feet, equal to the city’s annual water demands in 1924. To accomodate this second increase in reservoir size, the dam’s
western wing dike was also extended by 600 feet. [Figures 1, 2]
The St. Francis Dam was completed in May 1926. Two months earlier, the bureau had begun diverting aqueduct water into the
reservoir, allowing it to rise nearly two feet per day until it crested one year later, only three feet below the spillway, in time for the
dry season. After partial draining during the summer and fall of 1927, the reservoir was again refilled, now to within inches of the
spillway, during the winter of 1927-28. It reached capacity on March 7, 1928, allowing water to be directed to the other city
reservoirs, which were all filled to capacity five days later. With the satiation of the entire city reservoir system complete, excess
water was diverted into San Francisquito Creek, which ran for the first time since construction began on the dam four years earlier.
[Rogers, 1995: 32-3] [Figures 3, 4]
The St. Francis Dam Fails

On the morning of March 12, 1928 damkeeper Tony Harnischfeger telephoned William Mulholland with a disturbing report: he had
noticed leakage on the dam’s western abutment. This leak was different in character from the seepage observed in the dam’s
downstream face since the reservoir was filled to capacity five days earlier. Harnischfeger described the leak as muddy. To a water
engineer, this condition suggested hydraulic piping, the process of soil washing out from under a dam’s foundation.