Okla. Stat. tit. 45, § 45-747: Backfilling, compacting, and grading

The operator shall backfill, compact where advisable to insure

stability or to prevent leaching of toxic materials, and grade in

order to restore the approximate original contour of the land with

all highwalls, spoil piles and depressions eliminated unless small

depressions are needed in order to retain moisture to assist

revegetation or as otherwise authorized pursuant to this act.