And I can't really agree with you on this one.
It's not some sign composed by some faceless "burrocrat." The architect herself made the sign, which makes it part and parcel to the landmark, and the creator is no longer around to make a new (politically) grammatically correct one. Score one against the Prescriptivists!
From the Wikipedia articles, her employer seems to have been a stickler for details. Somehow, I'm sure someone must have pointed the errors out to her long ago, and I'm just as sure she told them what to do with their proverbial red pencil!
But you should keep yours in your pocket on this one!
What makes the place a national landmark is IMHO the awesome power of what Nature hath wrought ...
No, that's what makes the Grand Canyon a National Park. The time period and details of its construction, the details of its design, decoration, and integration into the landscape, and who its creator was is what makes it a National Historic Landmark.
You gotta admit, "emense" is pretty far off. It could and would be assumed by readers to mean some descriptor they'd never heard before. This one wasn't even addressed, no doubt akin to the dilapidated building that isn't repaired because it's just too much work.
Well, yeah, but the first 'e' is separated from the second by a single consonant, so the rules of pronunciation would give it a long sound (ee-mense), close to imense, but not close enough for government work (although a government contractor would undoubtedly try to slip it through and charge extra to correct it later rather than fix it in the first place).
And it was addressed by the defacers:
The misspelled word "emense" was not fixed, Deck wrote, because "I was reluctant to disfigure the sign any further."
(emphasis added)
In his own words, he admitted that he was disfiguring the sign.
but methinks they overreacted in the penalty
Are you kidding?
... were sentenced to probation and banned from national parks for a year.
No jail time, no fines; just a year to stay out of the National Parks and cool off. My heart bleeds for them.
... have one taken from a stage that says "Basin Street Sheiks" but it's not going to get any bids on eBay. (It is however spelled correctly). ...
I've heard your sound clips. Isn't there an 'r' missing in the third word of your sign?
... underreacted in failing to acknowledge the error itself or explain why it was left in place so long or even accepted in the first place. ...
Probably because the original owner (either the Fred Harvey Company or the Atchison, Topeka & Santa Fe railroad) left it that way.
I have to suspect that the government entities in charge think as highly of their sign as of the Canyon itself. If that be the case I must question their qualifications as caretakers.
I suspect they think as highly of the sign they inherited as they do of the tower and the entire site they inherited.
It's unclear to me whether the site is owned by the Federal Government, some Arizona State or Local entity, or some other entity.
Here is a
page from the National Park Service. It's page 9 of the 23-page Property Documentation Form that submitted/approved the Desert View Watchtower site to the National Register of Historic Places. It gives some background into when and why it was built by the Atchison, Topeka, and Santa Fe railroad for use by the Fred Harvey Company. Click on the Pan Left/Right/Up/Down links on the right of the image. You can also go back and forth to other pages, but you'll have to click Zoom In for each page. It's still an interesting read!