Unless separately incorporated, wholly-owned mining company railroads are excluded from the database.

Mining operations that move tremendous tonnages frequently depend on rail transportation. This includes mining operations as diverse as copper, iron, limestone, and certainly coal mining. In the majority of cases, railroad operations are restricted to small numbers of privately-owned locomotives working on privately-owned tracks.

A few types of mining operations such as taconite in Minnesota, copper in Arizona, gilsonite in Colorado and borax around Death Valley had to move across large expanses of non-company land. In most of those cases, companies separated their rail operations into closely-held corporations and normally included some variation of the word "railroad" in their names.

Ideally, I try to include only those operations which were officially incorporated and which included some variation of "railroad".

I originally made a few exceptions where information suggested the rail operations might have operated seperately from their mining company parents. These days, I eliminate most of those remaining companies when I find them.

I also leave a few mining-related companies in the database simply because no good confirmation of full company names has ever emerged to cause me to either include or exclude those names.