The quake had a depth of about 16 miles, USGS reported. Shaking was felt throughout the Ventura County region as well as various parts of Los Angeles County.
No injuries or damage have been reported.
USGS initially reported the quake as a magnitude 3.9 before upgrading it to 4.1, then adjusting it to 4.0.
"Felt it big time in East Ventura -- three hard shakes and some rolling," said Jennifer Diane on Facebook.
Caltech seismologist Dr. Lucy Jones, noted on her Twitter page that Saturday's quake "is in essentially the same location as the M3.9 on Feb. 11. Both are very deep for Southern California."
An magnitude 3.1 aftershock was recorded at 8:44 p.m. about six miles northwest of Santa Paula. That quake had a depth of 11 miles.