Who mapped these? In New Mexico we have a ton of dry arroyos that maybe have a couple inches of flowing water a few times a year. Zooming in at places I'm familiar with, a surprising number of them are mapped. I know of rez roads[1] nearby that aren't on OSM or any map I know of, but the ditch we used for cross country practice is. Wild!
[1] Two-track dirt roads on the Navajo Reservation that are not regularly maintained, or officially numbered/named but which are actively used.
[1] Two-track dirt roads on the Navajo Reservation that are not regularly maintained, or officially numbered/named but which are actively used.