It is pretty simple. Draw two lines on a sheet of paper in a big cross. Easy enough right?
Now start at top left and going clockwise label the four quadrants A, B, C, and D.
A and C are private property. B and D are public.
Now lay a dime on the paper and slide it from D to B without getting onto A or C. Not Possible!
But could you walk your fingers across that sheet of paper without touching A or C. At 4 Corners NM, is it possible to step from NM into UT without ever stepping into CO and AZ?