Unfortunately, the split mineral and surface rights on this property really do complicate things. As much as I want this easement to go through, there may actually be some prudence involved here. Because the mineral rights are separate from the surface rights in this case, a conservation easement by the surface owners could not prevent a well from being drilled on this property (or other mineral extraction such as coal, etc). Theoretically, at least, if the mineral rights owner wanted to develop this property, the surface rights owner could not entirely prevent them from doing so. Typically, what happens if a well has to be drilled on land leased by the mineral rights owner, but not agreed to by the surface rights owner, is that a court will decide a level of compensation due the surface rights owner. So the worst case scenario here, is that the easement is approved, this area becomes a hotbed of oil and gas activity, and the mineral rights owner leases their rights, which allows wells to be drilled in spite of the conservation easement.
I encourage everyone to read
http://www.leg.mt.gov/content/publications/Environmental/hb790brochure.pdf and see how little protection this easement would actually provide against mineral development.
Now, with modern technology, it's easier to reduce the surface footprint from subsurface mineral extraction (long lateral wells), but that doesn't guarantee there wouldn't be surface disturbance. $6 million is a lot of money to spend on a conservation easement that doesn’t actually guarantee the land cannot be developed.