Sorry for the delay. Website crashed for a while. These are my thoughts:
1. HR doesn't want to be accused of disability discrimination.
2. HR doesn't want to pay your unemployment insurance benefits (which, to be fair, are probably pretty small, because you don't have much credit left after not working for nine months).
3. HR doesn't want you to quit, because if you do, then HR must pay out the vacation and holiday hours time at your current pay rate, within 72 hours of your termination notice. Cal. Labor Code Sections 202(a) and 227.3. Also, by your quiting, HR can claim that it has no liability for unemployment insurance benefits. And, HR can claim that it was trying to find you work, but you took that option away by quitting.
So, HR's best move is to do nothing and let you react (or, at least that's what HR believes -- I don't know if I would agree, but I'm not working for Six Flags, and I don't have all the inside info to completely evaluate the risk). Given that you can't go without employment, eventually you will have to find another job, and when you do, HR will react accordingly.
The question here is whether or not there really is work available, but your employer doesn't want to disclose it, because it would prefer that you quit and move on, since you're a potentially expensive health care liability. That would be unambiguous disability discrimination. If you could prove that such work exists, then you have a pretty solid legal action. If the business has a website where jobs are posted, then you may want to take a look. You may also want to visit the park (I assume your employee id is still valid -- otherwise, you're not an employee), and talk to some coworkers to see if there are any jobs. That could cause HR to get nervous, if and when it gets back to the office that you're snooping around. But, you could do it, and try to shake the branches.
Ultimately, if you're frustrated, then you can file a complaint with the Department of Fair Employment and Housing (DFEH), and let them investigate for you. Or, you can hire an employment rights attorney and let him/her try to push a little fear of legal action.
I think that about covers the issue. If you need a link to the DFEH website, or to a lawyer referral service, or you have other questions or concerns, please let me know.
Hope this helps.