Car went over temp after about 30 minutes of driving. What could this be?

Check for correct fluid level first of all in the radiator,, if the fluid level is fine, you may have a stuck thermostat,, or a fan relay thats not turning the fan on at the desired temp, , start the vehicle and look for a couple of things,, 1 remove the radiator cap prior to starting the motor, ( make sure before you do this that the motor has cooled down) let the motor run so it will warm up,, 2 things to look for,, fluid movement in the radiator once it heats up,, you can look into the radiator cap opening to see this happen, and 2 watch for the fan to come on, If you have ac ,,and a single motor,, leave the ac off, if you have 2 fans on the vehicle, turn the ac on , check to see if that fan started, if so turn that one off , if the fan comes on once heated enough,, the fans are ok, if you see movement in the fluids in the radiator, then the thermostat should be ok, They are cheap and easy to change, so if your not sure, Just replace that part