The bad news is that your employer can require you to work more than 40 hours a week, and this is true whether or not you are salaried.
The good news is that unless you are "exempt", your employer has to pay you overtime if you work more than 40 hours in a week. Many employers make the mistake of believing that "salaried" means "exempt". This is not so. Whether you are exempt depends on what kind of work you do. If you are a professional (what is a professional is defined by statute), a manager with authority to make substantial decisions, or one of several other groups of employees, you may be exempt, in which case you are not entitled to overtime. Without knowing what you do, I could not even make a guess whether you are exempt or not. However, you may want to check (you can look this up on the Department of Labor and Industry's web page, or you could call them and ask).
If you are salaried, your rate of overtime pay is calculated based on what your hourly rate would work out to be if you worked 40 hours per work and adding 50%. To make things very simple, if your salary worked out to be $1000 per week, that would work out to be $25/hour. Your overtime pay would be $37.50/hour.