The U.S. Geological Survey reported Wednesday that the system gave 35 seconds of warning to seismologists in Pasadena ahead of incoming seismic waves from the magnitude-4.7 quake centered in Riverside County, near Anza, just before 10 a.m. PDT Monday.
The quake shook a wide swath of Southern California, but did not cause serious damage.
The system has been broadcasting alerts to scientists' computers for several years, but is not available to the public at this time.
The Early Earthquake Warning project is being run as a test of a proposed statewide program that would use thousands of sensors already in place to notify people about imminent shaking from moderate to strong earthquakes.
Researchers want to create a system similar to ones that exist in Japan, Mexico and other quake-prone nations.
Proponents say having a few seconds of warning gives enough time for trains to stop, utilities to shut off systems or children to dive under desks.