Thanks first of all to Kruger for this enjoyable puzzle!
The pairing of the clues – i.e. knowing that one of each pair would be in the top (what eventually turned out to be the Northern) half and the other in the bottom half – was a clever and interesting technique, especially given its thematic relevance that was finally revealed to us near the end.
Fortunately (for me) I solved Clue 1 very early on, which hugely reduced the number of options available.
Ignore mass in principal characteristics putting Earth in deviations from orbital motion (12)
That looked like (m)AIN QUALITIES with E(arth) inside of it. With the first A being the extra letter to be removed, that gave INEQUALITIES. A quick check in the BRB confirmed deviations from orbital motion as a lesser-known meaning of INEQUALITIES and I was properly started.
It looked like the four 4-letter entries would really help next, given two of them started with the first I and U of INEQUALITIES. I’d solved three of them but wanted the fourth to double-check I had them right and thus where they fitted in the grid. I then twigged that Jock’s ankle was CUIT, leading to UNIT as one of the entries.
However, I didn’t spot what the hidden guidance was saying – namely ANSWERS CONTAINING N TO THE TOP AND S TO THE BOTTOM until I had perhaps only three left to enter into the grid. Nonetheless it did still provide a useful cross-check of what I had entered.
And I spent a long while on my LOI, which was VILLOUS. The definition was so accurate – with long, soft hairs – that I was almost certain of the answer very early on but I simply couldn’t make the wordplay fit. Eventually I hope I got it right with VILL(a)[N]OUS, a spelling of VILLAINOUS of which I was not previously aware!
As we owned our first house in Watford, then the circled letters seemed to make sense pretty quickly – thankfully no relation to the ‘Watford Gap’ of Motorway (and childish but funny Roy Harper song) fame.
And the Title? I am assuming that The Rockies are seen as the East-West divide in North America -and thus the ‘Not’ in describing this puzzle? Though I may have missed a whole layer of thinking here – not entirely sure!
Thanks again – most enjoyable!
Tim / Encota