Subject says it all. For instance, here in Southern California, the NDB
Petis is on the low chart, while ElMonte is not. Anyone know why?

Is it because of monitoring, or lack of? Or is it because one is part
of the enroute structure, and the other one not? Or because one has
approaches involving this NDB, but the other doesn't?

Anyone know for sure?

Cheers,
Addy