Which reminds me. Has California the legal right to legalize pot when other states lock people up for dealing in it?
Here's the way it works (or doesn't) under our system: California -- or any other state -- has every constitutional right to pass a law decriminalizing or even legalizing pot. All that means is that you will never be arrested by a local police officer or tried in a state court. However, the Federal government, if it so chooses, can have the FBI or DEA or ATF agents arrest you and you can be tried in Federal court on Federal drug law violation charges. As a practical matter, this doesn't happen because the folks in Washington don't really want to antagonize the voters of any particular state.
What other significant variations are there in the legal right of states to make their own laws?
As long as a law does not violate the precepts in the US Constitution, the states not only can but, in fact, do enact virtually all their own laws. Federal statutes are supposed to address only relations between the states. However, I think that you can appreciate that where the Feds feel they have a vested interest, they manage to steer the states into thinking their way. They have a very powerful weapon. It's called money. Case in point: all the states now have a legal drinking age of 21. There is no state where a person under 21 can legally purchase any alcoholic beverages. Wasn't always so. Some states used to have a drinking age of 18. The Feds thought that raising the drinking age would help diminish the number of people killed in car crashes due to drunk driving. Now, there is no mechanism in the Constitution which would allow the Congress to pass such a law and make it manadatory for all 50 states. Each state has its own laws regarding such matters. However, all the states rely heavily on Federal highway funds to keep their roads in good repair. Without this annual money from Washington, some states would have difficulty keeping any roads open. Solution is simple. States are told, in effect: "You don't raise your drinking age to 21, you get no monay next year for road repair."
This sort of thing gives the powers in Washington a teriffic edge. It applies to school curricula as well. You teach evolution, we cut off your funds for education. (No, no, that hasn't happened yet, just an example of what's possible.)