I don't think it's anything like what you have done with IRS.  They ask for extensions of the statute when the audit has already made enough progress to identify issues, but requires more work on legal research, or substantiation, or both.  What California apparently does is ask for the extension at the same time the audit begins.  They do that, probably to cover as many years as possible. 

The threat is that they will propose an assessment of some outrageously high amount.  Depending on appeal rights, you might want to call their bluff. Or, you might decide instead to move to Arizona (which seldom audits anyone) or Oregon (which doesn't have a sales tax).