My question is, in the state of Utah, can employers do the following: if I take 8 hours of vacation on Monday and then work four 10 hour days on Tues, Wed, Thurs and Fri, can my employer pay me for 48 hours of straight time? Our overtime policy is that we are paid overtime after 40 hours.

Under Federal law, you do not have a right to be paid overtime until you have WORKED over 40 hours in a week. Overtime is not calculated on hours paid; it is calculated on hours worked. Nor does any state law require that paid leave time be included in overtime calculations.

In the example you provide, paying 48 hours of straight time is correct.

Thank you very much for your quick response.