I'm not sure what clause you're referring to but would such a clause even be necessary? The fact that federal government land belonged to the federal government is pretty much a given. And the only entity that can dispose of that land is Congress.
It is in the Nevada State Constitution: http://www.leg.state.nv.us/Const/NvConst.html
Under the section called Ordinance.
The clause was demanded by congress in order to prevent any claims that may have flowed from either Spanish rule or Mexican rule of the lands prior to the treaty of Guadalupe Hidalgo.