Replying to My job is making me work overnights

So I was hired for a valet positing up and Park City Utah back in October for full time/full season. When I was hired, there was NO mention of me having to work overnights. Before I took the job, I had two other job opportunities for the ski season. I decided to take the valet job at the hotel and told the other two places that I had found other work. Four days into this valet job I find out that I'm working a few overnights. At this point I had already committed to the hotel, and had told the other places I would not be working for them. I sucked the overnights up because they said it was just going to be temporary. So about a month after I was hired, they finally hired a new overnight. But they hired someone with two other fricken jobs AND kids, and paid her $8.50!!!!! During they day valeting cars, we tend to bring in over a $100 in tips making the job well worth it. Overnight however is lucky to make $20 in tips on a good night. So obviously the new overnight lady quit after a month. So now we are stuck doing overnights again. This is BS. Overnight is a separate job. If they told me I would have to work some overnights before they hired me, I NEVER would have taken this job because I have 3 loud roommates and there is no way I could ever sleep during the day. I would LOVE to just quit this job, but I live in a ski town and at this point, it would be very hard to find a new job. So basically I'm wondering if I have any sort of workers rights or is it perfectly legal for them to hire you, not mention that you might have to work overnights, and then start having you work overnights? Any info would be appreciated because I plan on talking to HR and would like to know my workers rights and all.