Andy,
See if this link was the one.
http://www.coloradoprospector.com/forums/i...hl=private+landIt doesn't really change any of the answers, but it does try to work through how RS 2477 does and does not apply (and the room for interpretation is pretty wide between judges). The bottom line of it is that it would be very difficult to guarantee an outcome with use of this specific law as basis to overrule the rights of a private land owner. Without the private land owner's approval, this would probably have to be resolved in court, with a great deal of burden of proof (and numbers you probably won't be able to produce unless that road is being used on a regular basis by the public ... which it sounds like it isn't) falling to your company.
It would be a risk, something I wouldn't even bother trying on a road that is claimed as private but nobody has shown any intent to use except by your company; but maybe your corporation's legal counsel can help you decide what route you'll ultimately be taking from this point, and/or knows something we don't. (And if they do end up knowing that something, please let us know!)
Swizz likely has the right of it: resources might be better applied by creating an access, either by leasing access rights to the road from the owner, or filing plans/building a new access on public grounds. Naturally, the cost of either means of creating that access will have to be weighed heavily against the minimum expected yield of the claim (which means you'll want a geologist to weigh in on the claim's yield value, presuming your company doesn't like to take "wildcat play" risks on prospecting/mining.)
It's a tough answer, but this is why it is so important to establish proper access while researching any area to claim. And when you are requiring operating with a profit yield, that access is much more important from the standpoint of costs of impact should the road be lost for use. Most companies will ensure they have taken steps to ensure those roads stay available, either by working with the county or any existing land owners with leases... and naturally, that work would probably prove an ongoing effort for the life of the mine.
Unless you have proof for certain that the road is open to the public, I would be hammering away at a lease deal with the private owner that provides said owner a comfort level that their land is protected, speaks to any misgivings they may have, gives them enough of a taste for granting access (ie, pay them enough so they will feel inclined to renew the deal later), and finally gives your company guarantee of access (at least along that stretch of road) for a specific length of time.