Uranium ore when mined from the ground is of little use for nuclear purposes (such as nuclear power plants and nuclear weapons). The ore has many impurities and must be concentrated.
The milling process removes non-uranium material and results in a concentrated mixture of uranium oxides, predominately U3O8. Early in the milling process, the material has a yellowish color, thus resulting in the name "yellowcake."
Iran has its own uranium mine and a uranium recovery facility (where yellowcake is produced) at Ardakan near the center of the country.
The United States has uranium recovery facilities (produces yellowcake) in Colorado, Nebraska, New Mexico, Texas, and Wyoming.