Not an easy question to answer, as the UP runs through quite a number of different areas. The following picture of Pelle Soeeborg´s famous Daneville & Donner RR may give you an impression of what the ballast the UP uses in arid areas could look like:
Walthers kits are made of polystyrene, so any type of liquid plastic cement should work .
as a Uk railroader advise please on suitable ballest for UP region i hope to use woodland scenics products
also what type adhesive best for walthers kits
mike uktrainnut uk