We have large chunks of BLM and Nat Forest land with partial sections of private land scattered around through them, usually surrounding a spring but sometimes being just a rock pile. I can't explain how some of those pieces ever got claimed. Likewise, there are huge chunks of private land with pieces of public land in them, often with no public access. Anyway, even federal employees don't know where the boundaries are without some kind of instruments to locate them. OnX is a big help.
