Via KCRA.com: Polio-like disease reported in all parts of California. Excerpt:
Data released Monday show that a mysterious, polio-like disease that has paralyzed at least 20 children has been present throughout California since 2012.
The data were released by the California Department of Public Health in response to a public documents request by KCRA 3.
A one-page document shows that the greatest number of cases, six, has been reported in the part of Northern California outside the Bay Area.
Click through to see the table (which I can't reproduce here). Strikingly, the first cases were all reported on three days in mid-September, 2012: northern and southern California on September 12 (2 cases), southern California on September 13 (1 case), and central California on September 14 (1 case).
The report also notes that a case reported on December 28, 2012 was that of a resident of another state who was hospitalized in California. But we don't know any of the circumstances of that case.