[rmk]

There is some nuance to this. CA deliberately defines anybody who is in CA "other than for a transitory purpose" as a CA resident (for tax purposes). So if you happen to reside in TX but come to Redwood City for a couple weeks and work there, for example, CA can come after you. I am fairly certain this will happen more often once increasing numbers of people vote with their feet.

[throwawaygulf]

Even this is not entirely correct. They do not consider you a CA resident, but they consider the income you make while (more than transiently) in the state taxable.

Many states have similar clauses (NY, NJ, etc.), CA is not unique in this aspect.

[dragonwriter]

CA is actually more generous than a number of states, which do not exempt transitory presence for work, so if you do earn any money at all for work while in the state you owe income taxes (and your employer is obligated to withhold for the State.)