### Question
How does the law define mandatory class I Federal areas?


### Answer
Under *42 U.S.C. § 7491*, **mandatory class I Federal areas** is defined as:

> Federal areas which may not be designated as other than class I under this part

#### Citation:
  - *42 U.S.C. § 7491*
  - Heading: **SUBCHAPTER I-PROGRAMS AND ACTIVITIES > Subchapter Referred to in Other Sections > Part C-Prevention of Significant Deterioration of Air Quality > subpart ii-visibility protection**

