"The Watchers"

'The Warning" The St. Francis Dam memorial by sculptor Eric Richards

Wiki:

"The St. Francis Dam was a concrete gravity-arch dam, designed to create a reservoir as part of the Los Angeles Aqueduct. The dam was located 40 miles (64 km) northwest of Los Angeles, California, near the present city of Santa Clarita.'

The remains of the The St. Francis Dam

Three minutes before midnight on March 12, 1928, the dam catastrophically failed, and the resulting flood killed more than 600 people. The collapse of the St. Francis Dam is one of the worst American civil engineering failures of the 20th century and remains the second-greatest loss of life in California's history, after the 1906 San Francisco Earthquake and fire.

Two motorcycle officers frantically raced through the streets of the city that night, sirens wailing, to warn sleeping residents that the wall of water was fast approaching. The first officer was Thornton Edwards (who until that moment have never even heard of the S. Francis Dam) afterwards nicknamed “The Paul Revere of Santa Clara”. Officer Edwards was later became the city’s police chief. The second officer Eddie Hearne, raced up the Santa Clara River valley towards the oncoming flood to warn the residents. Both officers survived their adventures.

The plaque at the base of the monument reads:

"Minutes before midnight on the chilly evening of March 12, 1928, the St. Francis Dam failed.

The Dam's 200-foot high concrete wall crumpled and collapsed, sending billions of gallons of raging flood waters down San Francisquito Canyon, about five miles northeast of what is now the city of Santa Clarita. The avalanche of water swept 54 miles down the Santa Clara River to the sea. No one knows the exact death toll, but more than 450 people perished in the disaster.

Shortly before 1:30 AM on March 13, an urgent message of imminent disaster reached the night telephone operator in Santa Paula and was quickly relayed to police officers, city officials, and then homes of the lower portion of town.

Among the many heroes of the flood that evening were two motorcycle officers who rode through the night to warn the sleeping citizens in the low lying areas of Santa Paula that a torrent of water was about to inundate their homes. Their heroic efforts saved countless lives. Their wild ride that night was stopped at 3:05 a.m. when the wall of water swept through Santa Paula on its way to the ocean."