Wouldn't that fall under the "... and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States..." part of the clause?
And, by the way, Congress has permitted its power to be usurped by the Executive....the Interior Deptmt and the BLM
They gave the BLM the authority to manage the lands in 1976. They didn't give them permission to sell it.
The entire article is: http://constitution.i2i.org/sources-for-constitutional-scholars/federal-land-retention-and-property-clause/