I hunt these areas in the Colorado Mountains (and occasionally in flatland areas). I use old (1900's thru 1930's) railroad maps to locate sites. At many of these places, there is little left to tell you that there was anything there or not. Back in the older railroad days, they could not go more that 10 to 15 miles without a water tower - these places are listed on many of the older maps (that might have been pretty much all that was there). Some of the maps I found were amazingly inaccurate as to where things really are, but (as has been suggested), I use Google Earth to localize my search areas.
In the Mountains of Colorado, many of the more level 4WD access roads were old railroad grades. Things got buried when the graders came thru to widen the roads - looking for signs of settlements and old pictures will help you find sites (ie. lots of research).
These places (at least in the west) often were also places to load livestock. I have found mostly relics looking (since there tends to be a lot of iron trash at many of the sites). You never know what you will find.
