The rotten-egg smell appears to have largely dissipated Tuesday.
The South Coast Air Quality Management District took the samples late Monday in the Coachella Valley and near the Salton Sea, a massive saltwater lake 150 miles southeast of Los Angeles that could be the culprit.
They also took samples in locations farther from the sea and across the region.
Officials received 200 complaints about the pungent aroma.
A massive storm late Sunday could have stirred up decay from a recent fish die-off at Salton Sea, but air quality officials say they haven't ruled out other sources yet.