Impassable Marsh (historical)
Swamp in Humboldt County, Iowa · on the USGS Thor quadrangle
42.73747, -94.04051
Maps that show Impassable Marsh (historical)
Get them in the map app
Thor, IA
Detailed map of terrain, trails and roads
USGS topo, 2022
Fort Dodge, IA
Old map for history, not navigation
USGS historical 15-minute topo (1923)
Bureau of Land Management Eastern States Overview map
BLM Eastern States (2019)
IFR Enroute Low Altitude Chart L-12 (U.S.)
FAA, 2026-10-29
IFR Enroute High Altitude Chart H-05 (U.S.)
FAA, 2026-10-29
Nearby
Name, class, county and location: USGS Geographic Names Information System (public domain).