25 C.F.R. § 173.21
A permittee shall within 10 days after notification in writing of the cancellation of his permit by the Secretary, vacate the premises covered by the said permit. Any person occupying lands dealt with in the act of April 4, 1938 (52 Stat. 193) without an approved permit or lease shall be notified in writing by the project engineer of the requirements of this part and that for the failure of such person to comply with these requirements and receive a permit or lease within 60 days after receipt of the written notice shall constitute a willful violation of this part, and the project engineer shall submit promptly to the Commissioner of Indian Affairs a detailed report concerning the case, together with recommendations looking to the taking of appropriate legal action to remove such person from the area and to the collection of such funds to compensate for any use made of the property or damages suffered thereto.
25 C.F.R. § 173.21