91 miles. On the 77 kw day signal, it is quite listenable. Once outside my house in La Quinta, the 690 signal is quite usable and I am in more of their null than Mexicali is.
Santa Rosa and San Jose are both in the same US market, San Francisco. They are 99 miles apart.
They could, were the "border concept" be viable (very subjective from the offset), do what KOB in Albuquerque did with a synchronized repeater on 690 with something like 1 kw to 2 kw. The same could be done with all the way to Nogales and San Luis Río Colorado (Yuma) if they wanted. 690 is a shared Mexican and Canadian clear channel.
The XEWW null at about 50° is a sympathetic null created by the need to seriously limit the signal at about 130° to protect the primary Mexican station on 690 in Mexico City.
Of course, we are playing Fantasy Radio here... but it is an interesting radio and socioeconomic subject.