Is my employer required to pay the federal per diem rate if they send me out of town to work? I live in Colorado and they want to send me to South Dakota for a month. I have no contract with this company (I'm a tree trimmer), they will give me a company truck to use. They said the per diem is about $70-75. The GSA website says that lodging is $77 and meals, etc. is $51. Also, after that job ends, they want me to work in Cheyenne, WY (approx. 100 miles) for up to 3 years, and say there is no per diem for that job. I would have to use my own car and gas, etc. Are they supposed to pay per diem for that?

Your employer is free to negotiate any and all terms with you. As long as minimum wage is paid according to State Law (and other State requirements are met) there are no other requirements on the part of the employer.