That would depend on who created them. If they were original D&RGW folios and drawings, then the copyrights would belong to the railroad or it's successor, the Union Pacific depending on the year they were created. If the drawings were created by John Maxwell, or others, the copyright would belong to his heirs, if there are any. And if they're copies, the copyright belongs to whomever created the original.
And, of course, it would depend on whether or not you're making money from them, selling them outright, or selling advertising on your web page, if they're for educational use or fair use.
It gets trickier if someone obtained the originals and then published them in a book, and you have copies of the same originals. Or even the originals themselves.
There's a huge dispute going on in Academia right now, whether or not the rights to scientific projects funded by the Federal Government are owned by the researchers or are public domain.
Copyright law is extremely convoluted and complicated (Thanks to Walt Disney), and especially in the Digital Age (DMCA)..
I know that probably doesn't help much, but it might give you an idea where to start...
Robert