PRSL and other researchers

Heading for Denver this Septemeber for a few days and have cleared the schedule (wife) for a day of good old fashioned research........
Trying to remember where I was told to look in Denver ofr records of the uintah Railway, specifically tax documents, wreck reports, ICC evalutions, etc. etc.
Been to the DPL, not really helpfull with anything that has not been "cataloged".
Been to the USGS facitity, helpfull, but very little there.
Been to the CHS, but don't remember feeling like there was more there tahn what was on "display".
Seems like I remember George telling me about researching tax evaluation reports ate the state archives???
Any leads or flat out wild goose chases would be appriciated.
Rodger