Drain locations are holes in the soil used to drain excess water from the land surface to underlying tunnels. 

In the early 1900s after irrigation of the Twin Falls tract began, drainage problems occurred on the farmland. As a result, drains and drainage tunnels were constructed to drain excess flood irrigation water from agricultural fields by digging a hole from the land surface to an underlying tunnel. A series of drains in the field empties the excess water into the tunnels. These drainage systems pose risks of contamination to ground water and surface water by providing a direct conduit for contaminants associated with any development or changes in land use on or near the systems.