I have no check engine light and no codes. Took it to smog and it failed in the visual section for gross leak in evap system. I know about the charcoal cannister and that this is a vapor leak, but what are the most common causes and what is the sequence of steps to find root cause... oh yeah, and I'm California resident, hardest place to pass smog on the planet...

 

Did you ask the tech to show you the leak? Off the top of my head, a visible leak in the system would be a disconnected/torn hose or a hole/crack of some kind in the canister. To find the root cause simply start at the tank and follow the line to the canister. Check the connections to the solenoid and pressure valve as well.