The state is reporting 49 confirmed cases of measles so far in 2014.
Last year at this time there were just four.
This is the first year since 2000, when officials declared measles eliminated in the U.S., that the number of cases in California climbed above 40. And it's just April.
The California Department of Public Health says the highest number of cases - 21 - have been reported in Orange County. Other affected counties in Southern California include Los Angeles County with 10, Riverside with 5 and San Diego County with 4.
In Northern California the cases were spread out between Alameda, Contra Costa, Santa Clara and San Mateo.