The land the federal government has in Nevada was not purchased or taken from the state of Nevada after the fact by Congress - the federal government owned that land before Nevada was ever a state.
Also, the individual states are not sovereign, by definition.
Before statehood was granted, the land was occupied by settlers who had squatters’ rights. Why would statehood be necessary if the US already had jurisdiction and ownership???
http://usgovinfo.about.com/od/uscongress/a/statehoodproc.htm
The Typical Process
Historically, Congress has applied the following general procedure when granting territories statehood:
•The territory holds a referendum vote to determine the people’s desire for or against statehood.
•Should a majority vote to seek statehood, the territory petitions the U.S. Congress for statehood.
•The territory, if it has not already done so, is required to adopt a form of government and constitution that are in compliance with the U.S. Constitution.
•The U.S. Congress - both House and Senate - pass, by a simple majority vote, a joint resolution accepting the territory as a state.