RobL; Your time line seems confused. I can't account for MTDB meeting minutes.

Mexicans own line in Mexico. MTDB owns border to Plaster City.
CZRY started operating in Mexico when no Mexican operator steped forward. SDIY(V) was out then. Being semi-railfan they started fixing up the Gorge and after Mexico asked then to stop mining sand along the ROW began doing that in the good old USA.
We railfans went along with it because we like choo-choos. Also smarter minds at the Museum got then to stop using PSRMA units in their operations as PSRMA was supposed to tax-exempt. (time-line). Sand mining paid the way. Ocotillo city blocked truck access to a sand mine on Hwy S2 so Campo sand was the only game. When a bypass road was finished CZRY folded quickly afterward. Then PIR. Then BJRR in Mexico and now interest in the gorge. Still need fixing.