Houchins Narrows (“Hutchins Narrows” in some early literature, or simply “Narrows”) is a mostly breakdown-filled giant canyon passage (vadose cave passage) between Mammoth Cave's historic entrance and the Rotunda (= 1st cave room). It occurs at level B, the 2nd-highest level in the Mammoth Cave system. Cave passages at level B formed before 3.25 million years ago (during the Late Pliocene or before). When Houchins Narrows had flowing water, the underground flow path was to the northwest (toward the historic entrance and away from the 1st cave room - this is toward the Green River, the local base level).
Mouth of Mammoth Cave (looking NW) (vintage photograph) - Houchins Narrows extends from here, the historic entrance, to the Rotunda, the first cave room (behind the photographer). The rocks are Beaver Bend Member limestones (Girkin Ls.). The historic entrance of Mammoth Cave was formed when a surface stream valley intersected & breached Houchins Narrows.
The passage is named after the fictional discoverer of Mammoth Cave. The story of Houchins' 1797 discovery of the cave while hunting a bear is fictional. Houchins Narrows is relatively short (~0.15 miles) and extends to the southeast from the base of the entrance stairs. A locked door near the entrance stairs prevents access to the cave except for organized cave tours and special access by researchers and cave employees.
NPS locked door (looking SE, away from the cave mouth) - the horizontal slats help to restrict air movement & simulate what's perceived to be the original condition of this passage - rubble filled to near the ceiling. Air moves outward from the cave mouth during the warm summertime & inward during the cold wintertime.
The open spaces between the bars also allow bats to leave & enter the cave. Eight species of bats are known to inhabit Mammoth Cave. Bats were a common sight in Houchins Narrows in the 1800s (and in the Rotunda and Audubon Avenue and Little Bat Avenue, etc.). Bat populations used to number in the millions, but are significantly reduced nowadays.
Houchins Narrows (looking SE) - the ceiling of this passage is occasionally low enough to prevent upright walking for some people. Here, the rocks are limestones of the Beaver Bend Member of the Girkin Limestone, the same unit exposed along the entrance stairway at the cave mouth.
Houchins Narrows (above & below; looking at the southwestern wall) - the passage descends gradually toward the first cave room. So, the stratigraphic units along the walls get progressively older. Below the Beaver Bend Member (seen at the cave mouth & near the locked door) are the Bethel Member and the Paoli Member (both lower Girkin Limestone). The Bethel is a thin interval of dark, argillaceous limestone. The dark gray beds near the top of this photo are the Bethel. The gray limestone beds below that are the upper Paoli Member.
The dirt piles and rubble on the floor at the bottom of the photo are remnants of a saltpetre mining operation during the 1810s.
Houchins Narrows (looking at the northeastern wall) - this feature is artificial. It was carved out from the walls of Houchins Narrows & a vertical shaft connected this to the old visitor center. Mammoth Cave's air is about 54° F year-round, and the cave air cooled the old visitor center in the summertime. Natural air conditioning! This is no longer used.
Houchins Narrows (looking NW, toward the Historic Entrance) - this shows the passage cross-section shape of Houchins Narrows. An undetermined thickness of sediments, rubble, and debris has filled the passage, so it is not known how far down the original passage floor is. Houchins Narrows is the top portion of a giant canyon passage, so it originally formed above the water table. An underwater river flowed through this passage. Which way did the water flow? Available evidence indicates that water flowed to the northwest when the underground river was here.
The area to the left of the railing in the above photo is part of the 1810s saltpetre mining operation. Original wooden pipes are still on the floor here. The pipes are hollowed-out tulip poplar tree trunks (see below). These pipes delivered water from the entrance waterfall to leaching vats in the Rotunda & Broadway Avenue.