How can a place be simultaneously 4k elevation and also "presently below sea level"? Are you saying that the introduction of sea water would rapidly erode 4k ft of surface material?
But I also think he's wrong: as said in http://www.netstate.com/states/geography/mapcom/nv_mapscom.h..., I quote "[...] but the lowest point in Nevada is actually only 479 feet above sea level at the Colorado River at the southern end of the state." .