Legal Question in Employment Law in California

Since virtually all employment contracts in California are "at will" meaning the employer can let the employee go at any time, with or without cause, and the employee can quit at any time with or without cause. The effect of that is the employer can change the terms and conditions of employment at any time, since they can fire you if you don't agree to the change or you can quit if you don't agree. The only binding rule is that they can't change terms retroactively. So accumulated vacation has to be paid, and wages have to be paid at the rate agreed at the time the work is done - no retroactive pay cuts - but that's about it. Anything else can be changed with little or no notice. Therefore, since anything about duties can be changed, it doesn't really matter how they are described in the original employment contract.