Chicago is located in the Central Time Zone (CT), which is UTC-6. California, on the other hand, is located in the Pacific Time Zone (PT), which is UTC-8.
So, when it is 8 AM in Chicago (CT), it is:
8 AM CT - 2 hours (time difference between CT and PT)
= 6 AM PT in California
Therefore, if it is 8 AM in Chicago, it is 6 AM in California.