I've came across ubiquiti reading about community/urban mesh networking, but (unless you mean their "non-WiFi" - meaning non-802.11 - hardware) we're talking 100s of meters between nodes there, being reasonable maximum within unlicensed band limitations (although, in the past, I personally set up a 1.3km point-to-point link using off-the-shelf 802.11b access points and simple parabolic antennas). It would be a fascinating exercise to see what is possible with commodity hardware in wildnerness. Interestingly, my past experience suggests that foliage can be equally "lethal" to radio waves as man-made structures.
As to the meshing algorithms, I recently heard a talk from a gentleman working on some of the largest "Internet of Things" pilot projects (eg. city lighting management) claiming that the (existing) self-managing meshinging protocols, although working fine in a household setting (and possibly research labs) completely failed in dozens of thousands nodes use case and that more "classic" solutions with managed infrastructure are the only way to go. I'm curious what size of the network do you have in mind? 10s of kms may be a big distance between nodes, but I guess the areas covered can be even larger?