The Sacramento-Yolo Mosquito Vector Control District says the two species of mosquitoes that can carry the Zika virus have been established in California since 2011 but have now been detected as far north as Sacramento.
The two species of Aedes mosquitoes also carry other viruses harmful to humans, which is why technicians check on traps for them.
So far Zika virus, which was first detected in Brazil, has not caused any deaths and the symptoms may not even be detected by those who contract it.
But there are strong links to birth defects in women who in areas where there are outbreaks. Detecting the offending mosquitoes isn't the only concern.
Alerts have been put out to travelers to Central and South America to take precautions against mosquito bites.
"All it would take is one of those mosquitoes to bite that person and then it would continue making other people sick," said district spokesperson Luc Maria Robles.
Federal officials are also suggesting that pregnant women planning trips south of the border to postpone those trips.