Disposition of property on termination of permit.

Upon the expiration or other termination of the permittee's rights, in the absence of an agreement to the contrary, the permittee will be allowed 6 months in which to remove or otherwise dispose of all property or improvements, other than the road and usable improvements to the road, placed by him on the right-of-way, but if not removed within this period, all such property and improvements shall become the property of the United States.