The Effect of a Low Yield Nuke on a Steel Structure
The Ruth shot was a fizzle. The predicted yield was 1.5 to 3 kt, while the 200 ton yield was a fraction of that. Especially embarrassing to UCRL was that only the top 100 feet of the 300 foot shot tower was vaporized (though much of the remainder was scattered across the desert). It was standard practice at that time for each test to totally erase all evidence associated with it (automatically "declassifying" the site), which Ruth failed to do.
Hard to tell how tall this tower remnant is but I would guess about 100 feet, if the cross-sections are 10 feet apart (which would fit what looks like a ladder near the base).
Compare the above pic to this pic of the WTC1 core remnant (click to enlarge):
Note the wilted pieces of steel dangling down.
Note-- this puts the WTC destruction into good perspective. If a 200 ton yield nuke can vaporize 100 feet of steel structure, and destroy 100 feet or more of it, you can imagine the yield nuke that would be required to vaporize the innards of the 208 foot wide WTC while leaving the outer walls more or less intact. What's not clear is if there is a linear correlation between nuke yield and vaporization radius-- I would guess it's not perfectly linear.
(thanks to A.P. for the find)