I have two lists. BeamElevations and FloorElevations. How can I merge these into Elevations
Use Concat and OrderBy
var result = list1.Concat(list2).OrderBy(x => x.Elevation).ToList();
If you want to remove duplicates and get an unique set of elements you can also use Union method:
var result = list1.Union(list2).OrderBy(x => x.Elevation).ToList();
In order to make it work properly you need to overide Equals and GetHashCode methods in your class.