110 Exit
The 110 Exit is a natural sinkhole that collapsed and created the passageway to the surface. The increased airflow led to abundant growth of cave popcorn. Because the outside is close and there are more organics, the room is a great place to find cave life. 
Geology
Room Development
The 110 Exit is a sinkhole entrance. A sinkhole is a more or less circular depression at the surface and is associated with karst topography (Bates and Jackson 616). Acidic groundwater dissolved the marble, opening spaces underground. This process continued until the roof could not support the material above it and the ceiling collapsed inward. Since the collapse reached up to the surface, a sinkhole formed (Palmer 27-28).
Cave Formations
When the entrance was created, the air flow changed. Drier, oxygen-rich air was brought into the cave and carbon dioxide escaped. The outside air facilitated the growth of several kinds of cave popcorn and stopped the growth of draperies, seen on the left side of the room.
Ecology
The twilight zone here is an ecotone, the border between two different habitats and hence a place with the most types of species. These areas of transition are common on the Monument and in the region. The result is that Oregon Caves highlights 1) a great biodiversity due to high speciation and migration and low extinction (>300 species), 2) disjuncts (populations separated geographically from other populations, such as a centipede and a cricket), 3) endemics (species found nowhere else, such as grylloblattids, beetles, flies, millipedes, springtails), 4) relicts from the Ice Ages (grylloblattids, crickets) or dinosaur times (springtails, diplurans), and 5) species at the limits of their geographic range (a centipede and cricket).
The bigger a cave is and the more caves a county in the U.S. has, the more endemic and overall species it has (Christman & Culver. 2008). Such a correlation is likely because, the bigger a cave is and the more caves in a county, the more different and similar habitats are available and the more likely caves will have more entrances for organic input (the longer a cave the more entrances it tends to have). The highest biodiversity is found in mid-latitudes in Europe (42 to 46 degrees latitude) and in North America (34 degrees). These are areas where both high enough temperatures and enough rainfall produce the highest amount of organics (Culver et al. 2006). Evaporation and organic oxidation rates further south reduces the amount of organics available to enter caves. The high organics and nutrients (esp. phosphates and nitrates) in turn produce the highest density of caves and enough food and critical nutrients (1-2% of surface) to keep species from going extinct during prolonged droughts. Oregon Caves is somewhat to the north of the North American latitude mean of highest biodiversity. 
However, the abundance of soil animals (due to the variety of soil habitats) supplies an abundance of migrants that can become cave-adapted. These mountains are also very old and have low extinction rates underground. So the Caves has an abundance of endemics while the overall biodiversity (aside from microbes) is not all that high compared to caves in the mid-Sierras or the southeast (excluding the low cave diversity in the southernmost low lying areas such as Florida where most caves are at least partly submerged (fewer cave aquatics than terrestrials).
Bates, Robert and Julia Jackson, ed. Glossary of Geology. Alexandria: American Geological Institute, 1987.
Hill, Carol and Paolo Forti. “Speleothems: Carbonate.” Encyclopedia of Caves and Karst Science. John Gunn, ed. New York: Fitzroy Dearborn, 2004. 691-692.
Palmer, Arthur. “Influence of geology on cave patterns.” Cave Geology. Dayton: Cave Books, 2007. 27-28.
Roth, John. “Interpretive Manual for the Monument’s Showcave”. Cave Junction: Oregon Caves National Monument, 2011. 25-27.