43 C.F.R. § 3809.21 : Public Lands: Interior — REGULATIONS RELATING TO PUBLIC LANDS — BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR — MINERALS MANAGEMENT (3000) — MINING CLAIMS UNDER THE GENERAL MINING LAWS — SURFACE MANAGEMENT —GENERAL INFORMATION — When do I have to submit a notice?

(a) You must submit a complete notice of your operations 15 calendar days before you commence exploration causing surface disturbance of 5 acres or less of public lands on which reclamation has not been completed. See §3809.301 for information on what you must include in your notice.
(b) You must not segment a project area by filing a series of notices for the purpose of avoiding filing a plan of operations. See §§3809.300 through 3809.336 for regulations applicable to notice-level operations.

43 C.F.R. § 3809.21