There are hundreds of counties which have not a single Amateur in it, and maybe dozens of them even without permanent inhabitants. So we chased mobile stations.

I had a very good, detailed Rand McNally US road map (~60 pages),
And once I catch a mobile station not far from "tough" needed county - I used to give that US vehicle driver a directions, with road numbers and distances, asking him to go to that county, and "activate" it.
Counties usually have road signs marking county-line.
So the mobile just enter into new county, and makes a new, another contact with me. :)
Giving me one more. Step-by-step to 3144

Plus, it had to be at the right time of the day, on the right frequency band, to have a good enough radio-propagation conditions between USA and Europe.

It was a challenge.