Rivers come from Mountains. Nothing like out-wash alluvial fans.
I had to look up the term. I ran across some aerial photos. Very interesting. I would imagine geologists, paleontologists, archaeologists, gold prospectors, etc. might explore these features for clues about what the mountain might hold.
Incidentally, I was in Vietnam when Donovan's song hit the air. We were living in a valley surrounded by some spectacular mountains. Sometimes a mountain would be covered in mist or clouds and then it would reappear then disappear. That's what I thought the song was describing.