Same for me Joe. I am unaware of any taken down on the RR. Have you?
I am not surprised because of the habitat. They are not really cane / Tamarisk critters, and that's what is available for the most part immediately along the river west of Castalon. Along the roadway in Presidio county ditto. In the BB lowlands up the washes, and even places Terlingua Creek, I think the riparian areas that have expanses of more typical bairdi vegetation are too small and or isolated - but there are probably a gazillion areas that have not been checked?
Is it the vegetation that restricts them to higher elevation in these locals, or are the higher temps and lower humidity restricting that habitat? Then the question is, were the snakes forced up there with the habitat or are they doing something very different down low, and we just haven't seen them because we haven't looked? 
If you have a locality in Bexar county, or even better, a specimen maybe send it to Jim Dixon? I don't think it's in the book. Hope you are well Joe. H